CA2655995A1 - Method for providing traffic volume and vehicle characteristics - Google Patents

Abstract

Traffic monitoring and warning methods are provided herein. The method is for providing traffic volume, line occupancy, per vehicle speed and vehicle classification of vehicles travelling along a highway. The method of one embodiment of the present invention includes the first step of receiving acoustic signals created and radiated by the vehicles as they travel through a detection zone. The method of one embodiment of the present invention includes the second step of signal processing the acoustic signals. By the combination of these two steps, traffic volume, line occupancy, per vehicle speed and classification of vehicles are provided.

Description

(a) TITLE OF THE INVENTION
METHOD FOR PROVIDING TRAFFIC VOLUME AND VEHICLE
CHARACTERISTICS

(b) TECHNICAL FIELD TO WHICH THE INVENTION RELATES
This application is a division of application Serial No. 2,240,916, filed on June 16, 1998. This invention relates to traffic monitoring systems for monitoring commercial vehicles.

(c) BACKGROUND ART
Many kinds of systems have been disclosed which monitor and/or control traffic. Typically, each highway department had a command centre that received and integrated a plurality of signals which were transmitted by monitoring systems located along the highway. Although different kinds of monitoring systems were used, the most prevalent system employed a roadway metal detector. In such system, a wire loop was embedded in the roadway and its terminals were connected to detection circuitry that measured the inductance changes in the wire loop. Because the inductance in the wire loop was perturbed by a motor vehicle (which included a quantity of ferromagnetic material) passing over it, the detection circuitry detected when a motor vehicle was over the wire loop. Based on this perturbation, the detection circuitry created a binary signal, called a "loop relay signal", which was transmitted to the command centre of the highway department. The command centre gathered the respective loop relay signals and from these made a determination as to the likelihood of congestion. The use of wire loops was, however, disadvantageous for several reasons.
First, a wire loop system did not detect a motor vehicle unless the motor vehicle included a sufficient ferromagnetic material to create a noticeable perturbation in the inductance in the wire loop. Because the trend now is to fabricate motor vehicles with non-ferromagnetic alloys, plastics and composite materials, wire loop systems will increasingly fail to detect the presence of motor vehicles. It is already well known that wire loops often overlook small vehicles. Another disadvantage of wire loop systems was that they were expensive to install and maintain. Installation and repair required that a lane be closed, that the roadway be cut and that the cut be sealed. Often too, harsh weather precluded this operation for several months.
Other, but non-invasive, systems have also been suggested. US Patent 5,060,206, patented October 22, 1991 by F. C. de Metz Sr., entitled "Marine Acoustic Aerobuoy and Method of Operation", provided a marine acoustic detector for use in identifying a characteristic airborne sound pressure field generated by a propeller-driven aircraft. The detector included a surface-buoyed resonator chamber which was tuned to the narrow frequency band of the airborne sound pressure field and which had a dimensioned opening formed into a first endplate of the chamber for admitting the airborne sound pressure field. Mounted within the resonator chamber was a transducer circuit comprising a microphone and a preamplifier. The microphone functioned to detect the resonating sound pressure field within the chamber and to convert the resonating sound waves into an electrical signal. The pre-amplifier functioned to amplify the electrical signal for transmission via a cable to an underwater or surface marine vehicle to undergo signal processing. The sound amplification properties of the resonator air chamber were exploited in the passive detection of propeller-driven aircraft at airborne ranges exceeding those ranges of visual or sonar detection to provide 44 dB of received sound amplification at common aircraft frequencies below 100 Hz. However, this patent used only a single electro-acoustic transducer for receiving acoustic signals within a detection zone, and did not teach spatial discrimination circuitry for representing acoustic energy emanating from a detection zone.
US Patent No. 3,445,637, patented May 20, 1969 by J. M. Auer, Jr., entitled "Apparatus for Measuring Traffic Density" provided apparatus for measuring traffic density in which a sonic detector produced a discrete signal which was inversely proportional oniy to vehicle speed for each passing vehicle. A meter, which was responsive to the discrete signals, produced a measurement representative of traffic density. However, this patent used only a single electro-acoustic transducer for receiving acoustic signals within a detection zone, and did not teach spatial discrimination circuitry for representing acoustic energy emanating from a detection zone.

US Patent No. 3,047,838, patented July 31, 1962 by G. D. Hendricks, entitled "Traffic Cycle Length Selector" provided a traffic cycle length selector which automatically related the duration of a traffic signal cycle to the volume of traffic in the direction of heavier traffic along a thoroughfare. The Hendricks system did not teach the use of electro-acoustic transducers, but instead used pressure-sensitive detectors.
While Hendricks employed plural, non-electro-acoustic transducers, the traffic cycle length selector system did not include spatial discrimination circuitry.
Hendricks merely described the use of the output of several spatially discriminate detectors to generate a spatially indiscriminate signal.
There are, in addition, many other patents which are directed to systems which monitor and/or control traffic. Amongst them are the following US Patents.
3,275,984 9/1966 Barker 3,544,958 12/1970 Carey et al.
3,680,043 7/1972 Angeloni 3,788,201 1/1974 Abell 3,835,945 9/1974 Yamanaka et al.
3,920,967 11/1975 Martin et al.
3,927,389 12/1975 Neeloff 3,983,531 9/1976 Corrigan 4,049,069 9/1977 Tamamura et al.
4,250,483 2/1981 Rubner 4,251,797 2/1981 Bragas et al.
4,284,971 8/1981 Lowry et al.
4,560,016 12/1985 Ibanez et al.
4,591,823 5/1986 Horvat 4,727, 371 2/1988 Wulkowicz 4,750,129 6/1988 Hengstmengel et al.
4,793,429 12/1988 Bratton et al.
4,806,931 2/1989 Nelson 5,008,666 4/1991 Gebert et al.
5,109,224 4/1992 Lundberg 5,146, 219 9/1992 Zechnall 5,173,672 12/1992 Heine 5,231,393 7/1993 Strickland 5,315,295 5/1994 Fujii Specifically, some of these patents simply operated regular traffic signals or warning signs. US Patent No. 4,908,616 disclosed a simple system deployed at a traffic signal controlled intersection. A waming device positioned in the approach to the intersection at a "reaction point" gave an indication to a driver as to whether or not the driver's vehicle was too close to the intersection to stop safely if the traffic signal had just changed. The system did not measure vehicle speed and cannot account for differing stopping distances for different classes of vehicle. =
Systems which measure the speed of the vehicle included that disclosed in US
Patent No. 3,983,531, patented 9/1976, by Corrigan, which measured the time taken for a vehicle to pass between two loop detectors and operated a visual or audible signal if the vehicle was exceeding a set speed limit.
US Patent No. 3,544,958, patented 12/1970, by Carey, et al, disclosed a system which measured the time taken for the vehicle to traverse the distance between two light beams and displayed the measured vehicle speed on a warning sign ahead of the vehicle.
Conversely, US Patent No. 3,275,984, patented 9/1966, by Barker, disclosed a system which detected when traffic was moving too slowly, thereby indicating that a highway was becoming congested, and activated a sigo near a highway exit to divert traffic via the exit.
US Patent No. 4,591,823, patented 5/1986, by Horvat, disclosed a more complicated system using radio transceivers which were located along the roadway which broadcast speed limit signals by transceivers carried by passing vehicles.
Signals returned by the vehicle mounted transceivers enabled the roadside transceivers to detect speed violations and to report them to a central processor via modem or radio.
Traffic monitoring systems have also been disclosed which monitored various parameters of the vehicle itself to enable the class of vehicle to be determined. Thus, US Patent No. 5,173,692, patented 12/1992, by Heine, disclosed a system for controlling access through a gate or entrance according to class of vehicle and which used ultrasonic detectors to detect vehicle profiles and compared them with established profiles to determine the class of vehicle.

US Patent No. 3,927,389, patented 12/1975, by Neeloff, disclosed a system which counted the number of axles on a vehicle to enable classification of the vehicle and the calculation of an appropriate tariff for use of a toll road.
Systems (known as WIM systems) were also known which used sensors to weigh 5 vehicles while they were in motion so as to detect, for example, overweight commercial vehicles. Examples of such systems are disclosed in US Patents Nos. 3, 835, 945, patented 9/1974, by Yamanaka et al. ; 4,049,069, patented 9/1977, by Tamamura et al. ;
4,560,016, patented 12/1985, by Ibanez et al.; and 4,793,429, patented 12/1988, by Bratton et al.
US Patent number 5,008,666, patented 4/1991, by Gebert et al., disclosed traffic measurement equipment employing a pair of coaxial cables and a presence detector for providing measurements including vehicle count, vehicle length, vehicle time of arrival, vehicle speed, number of axles per vehicle, axle distance per vehicle, vehicle gap, headway and axle weights.
Lundberg, US Patent No. 4,109,224, disclosed a system which was concerned with traffic conditions and the difficulty a driver had in assessing a safe distance to the vehicle ahead, especially when there was fog, ice or rain. Lundberg's system had a series of "cat's eyes" in the road surface which served as both signalling devices and sensors for detecting vehicle presence. The Lundberg sensors merely detected vehicle presence and the processor, using the distance between sensors, then computed the speed of the vehicle. Lundberg's system detected the speeds both of a lead vehicle and a following vehicle and used "pre-programmed rules" to determine whether or not the following vehicle was too close for its speed. If it was, the processor lighted up the cat's eyes in the road ahead to warn the driver of the following vehicle to slow down. The maximum safe speed was obtained from a table which listed several different maximum speeds for different weather conditions. Lundberg's system merely selected a maximum speed from the table regardless of the type of vehicle.
Hengstmengel, US Patent No. 4,750,129, was directed to the production of an alarm signal on the basis of data obtained only from the speed of a vehicle which actually had overtaken a slower vehicle. Consequently, speed-limited signals were only produced by signal display arrangements to warn the overtaking vehicle if there was a real risk of a collision.
The known systems did not, however, deal with the fact that a particular site will not be a hazard for one type of vehicle, for example an automobile, but will be a hazard for a truck. When commercial vehicles, especially large trucks, are involved in accidents, the results are often tragic. Statistics show that, although commercial vehicles are involved in a relatively small percentage of all motor vehicle accidents, they are involved in a higher percentage of fatal accidents than other vehicles.
Consequently, they warrant special monitoring.
An invention, namely in US Patent No. 5,617,086, patented April 1, 1997 was previously made by the assignees of the present inventors provided an improved traffic monitoring system which was especially suited to monitoring commercial vehicles. That invention was concerned with assessing whether or not the site constituted a hazard for a particular vehicle depending upon its size, weight, speed and the like. The essence of that invention was to use a variable parameter (vehicle speed) and a fixed parameter (vehicle weight) to provide information relative to the maximum speed at which a hazard may be safely negotiated based upon the site-specific data of that hazard.
That invention was therefore concerned with the fact that a hazard (e.g., a particular curve, incline, controlled intersection, or the like) will not be a hazard for one type of vehicle, for example an automobile, travelling at a particular speed but will be a hazard for another type of vehicle, for example, a truck travelling at the same speed.
Recognizing this, that system had sensors to measure the weight and, if desired, one or more other physical parameters of the vehicle, e.g., height, number of axles or the like, and a processor for storing data specific to the site, e.g., severity of an incline, curvature and camber of a bend, or distance from the sensors to a controlled intersection.
The processor used both the particular vehicle data and the site-specific data to compute a maximum speed for that particular vehicle safely to negotiate that particular hazard. In essence, therefore, the system used the weight and, if desired, one or other more of the physical parameters of the vehicle to assess the forward momentum of that vehicle and to determine whether or not that vehicle can negotiate the hazard safely.

Several different embodiments of that invention were taught. One embodiment of that invention was directed to a traffic monitoring system which included a set of sensors which were disposed in a traffic lane approaching a hazard for providing signals indicative of the speed, and also indicative of at least the weight of a vehicle traversing the set of sensors. A processor had a memory for storing site-specific dimensional data related both to the hazard and to signals from the set of sensors. A traffic signalling device was associated with the traffic lane and was disposed downstream of the set of sensors, the traffic signalling device being controlled by the processor. The processor was responsive to the signals from the set of sensors for computing the actual vehicle speed. The processor also computed a maximum vehicle speed, which was derived from the site-specific dimensional data and from at least the weight of the vehicle. The computed maximum vehicle speed was thus the maximum speed for the vehicle safely to negotiate the hazard. The computed actual vehicle speed was compared with the computed maximum vehicle speed. The traffic signalling device was then operated if the computed actual vehicle speed exceeded the computed maximum safe vehicle speed.
Another embodiment of that invention was a traffic monitoring system for use in association with a traffic-signal-controlled intersection having a set of traffic signals and a traffic signal controller. The system included a plurality of sensors which were disposed in a traffic lane upstream of the traffic-signal-controlled intersection. The plurality of sensors included a final sensor which was disposed a predetermined distance in advance of the intersection, a preceding sensor which was disposed a predetermined distance preceding a final sensor in the direction of traffic flow, and a fiuther sensor which sensed weight of the vehicle for providing signals indicative of the weight of the vehicle. A processor was included which had a memory for storing site-specific dimensional data including the predetermined distance. The processor was responsive to signals from the vehicle weight sensor, from the preceding sensor, and from the final sensor to compute a predicted vehicle speed at the fmal sensor. From the site-specific dimensional data the processor then determined whether or not the predicted vehicle speed exceeded a computed maximum speed, at which speed the vehicle can safely stop at the intersection, should the traffic signals require it. If the vehicle cannot safely stop at the intersection, the processor transmitted a pre-emption signal to the traffic signal controller, thereby causing the traffic signal controller to switch, or to maintain, the traffic signal to afford right-of-way through the intersection to that vehicle.
Yet another embodiment of that invention provided a traffic monitoring system for determining potential rollover of a vehicle, The sensor comprised a set of sensor arrays which were disposed in a traffic lane approaching a curve and a vehicle height sensor. The site-specific data included characteristics of the curve, e.g., camber and curvature. The traffic signal device included a variable message sign associated with the traffic lane and which was disposed between the sensor arrays and the curve.
The processor was responsive to the signals from the sensor array for computing, as the vehicle speed, a predicted speed at which the vehicle will be travelling on arrival at the curve, and derived the maximum speed for the particular vehicle to negotiate the curve safely on the basis of vehicle parameters, 'including weight and height. The processor compared the predicted speed with the maximum speed and operated the traffic signal to display a warning to the driver of the vehicle if the predicted speed exceeded the maximum speed. Such a system could be deployed, for example, at the beginning of an exit road from a highway, between the highway exit and a curved exit ramp, and would warn the driver of a tall vehicle travelling so quickly that there is a risk of rollover as it attempts to negotiate the curve. In such embodiment of that invention it was necessary also to measure the height of the vehicle as it approached a curve, since the lateral momentum of the vehicle in the curve can be predicted to determine the safe speed at which the vehicle can negotiate the curve without rollover. Thus, the system of that invention computed a safe maximum speed for a particular vehicle in dependence upon, among other things, the weight and height of the vehicle.
Thus, the following systems have now been provided:
A truck rollover advisory system, which is a system designed to reduce truck rollover accidents which occur on highway exit ramps, in which in-road and off-road sensors determine individual truck speed, weight, height and type. From this real time data/information, the probability of a particular truck =rolling over is computed by a controller. A warning sign is automatically activated if an unsafe configuration is detected.

A downhill truck speed advisory system, which is a variable message sign to advise individual trucks of a safe descent speed prior to beginning a long downhill grade, in which, as trucks approach the downhill grade, a controller computes individual truck weight and configuration and determines the maximum safe descent speed for that particular truck using FHWA (Federal Highway Administration) guidelines. A
variable message sign displays the safe descent speed for individual trucks.

A runaway truck signal control system, which reduces the possibility of disastrous intersection accidents resulting from a runaway truck. As trucks proceed down a slope, the speed, weight and classification of each individual truck is determined. If the truck is travelling too fast to stop safely at the intersection downstream, a signal will be transmitted from a controller to the traffic signal lights. The lights will either hold or change to green until the oncoming truck travels through the intersection.

(d) DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION
While these systems have addressed the problems of truck rollovers, runaway trucks and downhill excess speed travel for trucks, some improvements are desirable. It would therefore be desirable to provide a system which made maintenance more efficient without unduly disrupting the traffic on the roadway. Thus, the systems of the prior art as discussed above, are expensive to install and maintain. Moreover, installation and repair require that a lane be closed, that the roadway be cut and that the cut be sealed. Often too, harsh weather can preclude this operation for several months.

The present invention provides in one broad aspect, a method for providing traffic volume, line occupancy, per vehicle speed and vehicle classification of vehicles travelling along a highway.

The method includes the steps of:

receiving acoustic signals created and radiated by the vehicles as they travel through a detection zone; and then signal processing the acoustic signals;

thereby to provide the traffic volume, line occupancy, per vehicle speed and classification of vehicles.

By one variant of this broad aspect of the invention, the method includes the step of using advanced signal and spatial processing to provide adaptive interference cancellation and high resolution multi-lane or multi-zone traffic monitoring, including shoulder activity.

By another variant of this broad aspect of the invention, as well as the above variant, the acoustic signals are received by means of non-contact, passive acoustic (listen only) above-road electro-acoustic sensor arrays which are mounted on overhead or roadside structures.

(e) DESCRIPTION OF THE FIGURES
In the accompanying drawings:

FIG. 1 illustrates an embodiment of one aspect of this invention comprising a traffic monitoring system which is installed upstream of a hazard for advising a driver of a detected truck of a safe speed for that truck to negotiate such hazard;

FIG. 2 is a block schematic diagram of the system of FIG. 1;

FIG. 3 is a flowchart depicting the operation of a first processor unit of the system of FIG. 2;
FIG. 4 is a flowchart depicting the operation of a second processor unit of the system of FIG. 2;
FIG. 5 is a flowchart depicting the subsequent processing of vehicle records for an optional embodiment of the system of FIG 3;
FIG. 6 illustrates an embodiment of a truck monitoring system which is installed upstream of a curve, for monitoring for potential rollover of trucks negotiating the curve;
FIG. 7 is a simplified block schematic diagram of the system of FIG. 6;
FIGS. 8A and 8B are flowcharts depicting the operation of the system of FIG.
6;
FIG. 9 illustrates an embodiment of another aspect of this invention comprising a truck monitoring system which is installed upstream of a curve of an off-ramp as a vehicle ramp advisory system to help prevent rollover accidents and out-of-control vehicles on sharp curves of freeway off-ramps;
FIG. 10 is a simplified block schematic diagram of the system of FIG. 9;
FIGS. 1 1A and 11B are flowcharts depicting the operation of the system of FIG. 8;
FIGS. 12 and 13 illustrate an embodiment of still another aspect of this invention in the form of a traffic monitoring system which is installed upstream of a traffic-signal-controlled intersection and operable to pre-empt the traffic signals;
FIG. 14 is a simplified block schematic diagram of the system of FIGS. 12 and 13;
FIGS. 15A and 15B are flowcharts depicting operation of the system of FIGS. 12 and 13;
FIG. 16 is a side elevational view of the mounting of electro-acoustic sensor array sensors forming essential elements of the systems of embod'unents of the present invention;
FIG. 17 is a drawing of an illustrative embodiment of an above-road electro-acoustic sensor array constituting an essential element of the systems of aspects of the present invention for monitoring the presence or absence of a truck in a predetermined detection zone;
FIG. 18 is a drawing of an illustrative microphone array for use in embodiments of an above-road electro-acoustic sensor array sensor constituting an essential element of the systems of embodiments of aspects of the present invention;
FIG. 19 is a block diagram of the internals of an illustrative detection circuit as shown in FIG. 17;
FIG. 20 is a detailed block diagram of a preferred embodiment of the above-road electro-acoustic sensor array constituting an essential element of the systems according to embodiments of aspects of the present invention; and FIG. 21 is a flow chart showing the operation of the controller block shown in FIG. 20.

(f) AT LEAST ONE MODE FOR CARRYING OUT THE INVENTION
(i) HAZARD WARNING SYSTEM
A generic aspect of the invention will now be described with reference to FIGS.
1 through 5. This generic aspect comprises a warning system which is installed at the approach to a hazard, whether it be a curve, an incline, a blind intersection, a traffic-signal controlled intersection, etc.
Referring to FIG. 1 and FIG. 2, the hazard warning system comprises, at a first sensor station, a first set of above-road electro-acoustic sensor arrays 1711, (namely, 1711A, 1711B) for detecting trucks by means of acoustic signals. The above-road electro-acoustic sensor arrays can determine whether the detected vehicle is a truck, or is not a truck, by an analysis of the sounds emanating from the detected vehicle. In addition, the truck may be classified dependent on its length, since the length of the vehicle can be determined by the length of time between the beginning of the detection of the vehicle and the ceasing of detection of the vehicle in its traversing through the detection zone of a known length. Finally, the speed of the vehicle can be determined by the length of time for the vehicle to enter the detection zones of the above-road electro-acoustic sensor arrays. The hazard warning system may alternatively include a first pair of in-road sensors 12, 13 which may be of the type which are embedded in a roadway surface in the left-hand and right-hand traffic lanes, respectively.
The in-road sensors 12,13 comprise vehicle presence detectors, and direct axle sensors which may comprise piezo-electric Class 1 sensors, or inductive loop presence detectors.
Each of these in-road sensors 12, 13 may also be used to determine the speed of the detected vehicle by the length of time for the detected vehicle to traverse the detection zone of a known length. While such in-road sensors may be used, suitable alternative sensors and detectors could be used, e.g., those disclosed in the patents cited in the introduction of this specification.
On-scale detectors (not shown) may be incorporated in each lane adjacent to each of the in-road sensors 12,13. The on-scale detectors ensure that the trucks passing over the in-road sensors 12,13 are fully within the active sensor zone of the in-road sensors and are not straddling a lane. The on-scale detectors effectively eliminate the possibility that a truck which was improperly classified will receive a message reconvnending a speed that is higher than is safe for that particular truck.
The above-road electro-acoustic sensor arrays 1711 assure that errors which may incur by a truck straddling a lane do not affect the safe speed calculation.
Therefore, such above-road electro-acoustic sensor arrays are important features of the warning system of aspects of the present invention.
A short distance downstream from the above-road electro-acoustic sensor arrays 1711A, 1711B, or the in-road sensors 12, 13, two traffic signal devices, in the form of electronic, variable message signs 14,15, are positioned adjacent respective left-hand and right-hand traffic lanes. The above-road electro-acoustic sensor arrays 1711A, 1711B, or the in-road sensors 12,13 and the electronic message signs 14,15 are connected to a first programmable roadside controller 16, which is conveniently located nearby. The programmable roadside controller 16 comprises a microcomputer which is equipped with interfaces for conditioning signals from the sensors, and an interface for transmitting a control signal to the respective message sign 14, 15 for the lane in which the vehicle is travelling. The microcomputer is preprogrammed with hazard site-specific software and data, i.e., specifically related to the location of the above-road electro-acoustic sensor arrays 1711A,1711B, or the in-road sensors 12,13 and the specific characteristics of the hazard, and truck classification data, which may be based, e. g. , on the length of the truck. It processes the signals from the above-road electro-acoustic sensor arrays 1711A, 1711B, or the in-road sensors 12,13, and determines, for each truck, information including, but not limited to, number of axles on the truck, distance between axles, bumper-to-bumper vehicle length, vehicle speed, truck class, which is based upon the number of axles and their spacings, and lane of travel of the truck. Using the hazard site-specific information and the truck classification information, the microcomputer computes an appropriate safe speed based on, inter alia, the class of the truck, and transmits a corresponding signal to the appropriate message sign 14, 15, causing it to display the safe speed while the truck passes through the region in which the sign can be viewed by the driver of the truck. The duration of the message is based upon hazard site-specific geometries and varies from site to site.
The microcomputer creates a truck record and stores it in memory, with the recommended safe speed, for subsequent analysis.
If the system cannot classify the truck accurately, e.g., when a truck misses some of the above-road electro-acoustic sensor arrays, or the in-road sensors by changing lanes, the system will not display a recommended speed. In such case, the variable message sign will display a default message, e.g., "DRIVE SAFELY". The default message is user-programmable, allowing alternative messages to be substituted.
Downstream from the electronic message signs 14,15 is a second set of above-road electro-acoustic sensor arrays 1711,(namely, 1711C, 1711D,) or in-road sensors (namely, 17,18,) which are the same as the first set of above-road electro-acoustic sensor arrays 1711 (namely, 1711A, 1711B) and in-road sensors (namely, 12,13), and so need not be described further.
These second set of above-road electro-acoustic sensor arrays 1711(namely, 1711C, 1711D), or in-road sensors (namely, 17,18), are provided in conjunction with respective lanes of the roadway approximately one kilometre (0.6 mile) beyond the variable message signs 14,15. These second set of above-road electro-acoustic sensor arrays 1711 (namely, 1711C,1711D), or in-road sensors (namely, 17,18), are coupled to a secondary roadside controller 19 to form a secondary sub-system. This secondary sub-system collects the same information as the primary sub-system, but it is used only for monitoring the effectiveness of the primary system.
As seen in FIG 2, the roadside controllers 16 and 19 are equipped with modems 5 20, 21, respectively, enabling remote retrieval of their truck record data, via a telephone system, by a central computer 23 in a central operations building (not seen).
Programmable controller 16 includes an AC or DC power line 16A, which is connected to an UPS 16B and to a power source 16C. Programmable controller 16 also includes a monitor 16D and a keyboard 16E. Likewise, programmable controller 19 includes an 10 AC or DC power line 19A, which is connected to an UPS 19B and to a power source 19C. Programmable controller 19 also includes a monitor 19D and a keyboard 19E.
Each controller 16, 19 may also have an interface or communications port enabling the truck records to be retrieved by, for example, a laptop computer. The system may also allow system operators to have full control over the primary sub-system of above-road 15 electro-acoustic sensor arrays 1711(namely, 1711 A, 171 1B), or in-road sensors (namely, 12, 13), including a disabling function and the ability to change the message on the variable message signs. The remote computer also has data analysis software providing the ability to take two data files (one from the primary sub-system and another from the secondary sub-system) and to perform an analysis on the compliance of the truck operator to the variable sign messages. Specific truck records from the two sub-systems can be matched, and reports can be generated on the effectiveness of the speed warning system.
The sequence of operations as a vehicle (namely, a truck) is processed by the system which is depicted in the flowcharts shown in FIG. 3 and FIG. 4, and subsequent analysis in the flowchart of FIG. 5. For convenience of description, it will be assumed that the vehicle is in the left-hand lane. It will be appreciated, however, that the same process would apply to a vehicle in the other lane. Referring first to FIG 3, which depicts operation of the primary roadside controller 16, when a vehicle passes under vehicle above-road electro-acoustic sensor arrays 171 1A, or over in-road sensors 12, the microcomputer receives a vehicle detection signal, step 3.1, and confirms, in decision step 3.2, whether or not the vehicle has been detected accurately. If it has not, step 3.3 records an error. If the vehicle has been detected accurately, and if no weigh-in-motion (WIM) scale is present, a typical weight and configuration of the truck is assumed. The microcomputer creates a truck record containing this information, namely, axle spacings and number of axles, length and electro-acoustic data, together with the time and date at step 3.4. If a weigh-in-motion (WIM) scale is present at 3.31, the actual weight, as well as other information, namely, axle spacings and number of axles, length and electro-acoustic data, together with the time and date is recorded at step 3.32.
Comparing the information with truck classifications which are stored in its memory, the microcomputer determines, in step 3.5, whether or not the vehicle is a truck. If it is not, no further action is taken, as indicated by step 3.6. If it is a truck, step 3.7 conducts a speed comparison of the actual speed with a nominal recommended speed, and accesses a truck class specific speed table to determine, for that truck class, a recommended safe speed for that truck safely to negotiate the hazard. In step 3.8, the microcomputer conveys a corresponding signal to variable message sign 14 which displays a "WARNING"
message. The truck driver is expected to gear down and to take due action as regard to nature of the hazard. Once the truck passes the variable message sign 14, steps 3.9 and 3.10 restore the variable message sign to the default message. The default restoration signal may be generated when the truck triggers a subsequent termination sensor, e.g., the second set of above-road electro-acoustic sensor arrays 171 1C, 171 1D, or the second set of on-road sensors, 17, 18, or a timer "times-out" after a suitable time-out interval.
Step 3.11 stores the truck record, including the recommended speed, in memory for subsequent retrieval, as indicated by step 3.12, using a floppy disc, via modem, a laptop or any other suitable means of transferring the data to the central computer for subsequent analysis.
After passing through part of the distance to the hazard, the truck passes the region of the second set of above-road electro-acoustic sensor arrays, (namely, 1711C
and 1711D), or the in-road sensors (namely, 17,18), and the secondary roadside controller 19 receives a vehicle presence signal, as indicated in step 4.1 in FIG 4. The secondary programmable roadside controller performs an abridged set of the operations which were carried out by the primary roadside controller 16. Thus, following receipt of the vehicle presence signal in step 4.1, it determines in step 4.2 whether or not the truck was accurately detected. If it was not, step 4.3 records an error. If it was, in step 4.4, the signals from the above-road electro-acoustic sensor arrays 1711C and 1711D, or from the in-road sensors 17,18, are processed to produce a secondary truck classification record, e.g., axle spacings, number of axles, weight, (if available), length, speed and other electric-acoustic data, together with the time and date. Using this information, and truck classification data which are stored in memory, step 4.5 determines whether or not the vehicle is a truck. If it is not, no further action is taken, as indicated by step 4.6. If it is a truck, step 4.7 stores the vehicle record in memory.
As in the case of the primary controller 16, the truck records can be downloaded to a floppy disc, via modem, a laptop or any other suitable means of transferring the data to the central computer for subsequent analysis to determine the effectiveness of the system.
FIG. 5 shows an optional flowchart for the analysis by the central computer, but only if a weigh-in-motion (WIM) scale is present. If such weigh-in-motion scale (WIM) is present, truck records are downloaded in step 5.1 from both programmable controllers 16 and 19 and are compared in step 5.2 to match each primary truck record from the primary controller 16 with a corresponding secondary truck record, i.e. for the same truck, from the secondary controller 19. The comparison is based on time, number of axles, axle spacings and length of truck. A matched set of records, as in step 5.3, enables a comparison to be made between the speed of the truck when it traversed the first set of above-road electro-acoustic sensor arrays 1711A, or in-road sensors 12, and its speed when it traversed the second set of above-road electro-acoustic sensor arrays 1711 C, or in-road sensor 17. Step 5.4 determines the percentage of trucks which decreased speed as advised.
The generic hazard truck speed warning system as described above, is not intended to replace runaway truck ramps, but to complement the ramps and potentially decrease the probability of required use of these ramps.
(ii) ROLLOVER WARNING SYSTEM
FIG. 6 shows the components of a traffic monitoring system, i.e., a rollover warning system, for detecting potential rollover of a truck approaching a curve, which is deployed between an exit 60 of a highway 61 and a curved ramp 62 of the exit road 63. The system comprises first set of in-road sensors 64, 65, namely station #
1 in-road sensors 64 and station # 2 in-road sensors 65, which are spaced apart along the left hand lane of the exit road upstream of the curve 62. In-road sensors 64, 65, which comprise vehicle presence detectors and axle sensors, are similar to those used in the first embodiment. A height detector 67, is positioned alongside the left hand lane.
The height detector 67 may comprise any suitable measuring device, e.g., a laser or other light beam measuring device. A traffic signal device, in the form of an electronic message sign 68, is disposed downstream from sensor arrays 65, 65A, and is associated with the right hand traffic lane, for example above it or adjacent to it. The exit road has two lanes and a duplicate set of in-road sensors 64A, 65A, 66A, a height detector 67A and a traffic signal device 68A are provided for the right hand lane. Since the operation is the same for both sets of sensors, only the set in the left hand lane will be described further.
Referring now to FIG. 7, the station # 1 in-road sensors 64, the station # 2 in-road sensors 65, the station # 3 in-road sensors 66, the overheight detector 67, and the electronic message sign 68, are connected to a roadside controller 69 which comprises the same basic components as the roadside controller of the aspect embodiment described in FIG, 1 to FIG. 5 above, including a microcomputer and a modem 70. The microcomputer contains software and data for processing the sensor signals to give vehicle class based on vehicle length, number of axles and axle spacings, and vehicle speed. The microcomputer is preprogrammed, upon installation, with data which is specific to the site, e.g., camber and radius of the curve, and the various distances between the in-road sensors and the curve. In use, the processor uses the site-specific data, and the truck-specific data which are derived from the in-road sensors 64, 65, 66, and height detector 67, to compute deceleration between the in-road sensors and to predict the speed at which the truck will be travelling when it arrives at the curve 62.
Taking into account height and class of the truck, and camber and radius of the curve, it determines a maximum safe speed at which that particular class of truck should attempt to negotiate the curve. If the predicted speed exceeds this maximum, implying a risk of rollover occurring, the processor activates the message sign to display a warning, e.g., "SLOW DOWN!" or some other suitable message. The sign is directional and is viewed only by the driver of the passing truck. The threshold speed is programmable and can be inputted or changed by the system user.
The sequence of operations as a vehicle is processed by the system will now be described with reference to FIG. 8A and FIG. 8B. When the vehicle passes over in-road sensors 64, 65, the resulting presence detection signal from the presence detector at sensor arrays 64, 65 is received by the processor in step 8.1 and the processor determines, in step 8.2, whether or not a vehicle has been accurately detected as a truck.
If it has not, step 8.3 records an error. If the vehicle has been detected accurately, and if no weigh-in-motion (WIM) scale is present, a typical weight and configuration of the truck is assumed. The microcomputer creates a truck record containing this information, namely, axle spacings and number of axles, length and electro-acoustic data, together with the time and date at step 8.4. On the other hand, if a weigh-in-motion (WIM) scale is present at 8.31, the actual weight, as well as other information, namely, axle spacings and number of axles, length and electro-acoustic data, together with the time and date is recorded at step 8.32. The micro computer uses this information, together with the time and date, to create a vehicle record. In decision step 8.5, from the information at steps 8.4 or 8,32, the micro computer compares the measurements with a table of vehicle classes to determine whether or not the vehicle is of a class listed, specifically one of various classes of truck. If it is not, the processor takes no further action as indicated in step 8.6. If decision step 8.5 determines that the vehicle is a truck, however, the processor determines in steps 8.7 and 8.8 whether or not the truck was also accurately detected at sensor array 65. If not, an error is recorded in step 8.9. If it is detected accurately, the processor processes the signals received from sensor 65 to compute, in step 8.10 the corresponding measurements as in step 8.4.
Station #2 may not be present in all systems, and, in such case, the system would then proceed from step 8.5 directly to step 8.14.
In step 8.14, the processor determines whether or not vehicle height is greater than a threshold value (e.g., eleven feet), If the vehicle height is greater than the threshold value, the processor proceeds to step 8.15 to identify it as a particular class of truck. If the height of the vehicle is less than the threshold value, step 8.16 identifies the truck type. Having identified the truck type in step 8.15 or step 8.16, the processor proceeds to access its stored rollover threshold tables in step 8.17 to determine a 5 threshold speed for that particular truck safely to negotiate the curve. In step 8.18, the measured speed at station # 1 is the speed of the truck when it arrives at the beginning of the curve 62. Step 8.19 compares the predicted speed with the rollover threshold speed. If it is lower, no action is taken, as indicated by step 8.20. If the predicted speed is higher than the rollover threshold speed, however, step 8.21 activates the message sign 10 68 for the required period to warn the driver of the truck to slow down.
Step 8.22 represents the sequence of steps which are taken by the processor to process the corresponding signals from sensor array 66 to ascertain the speed of the truck and the type of truck, and to create a secondary record. Subsequent transmission of the truck data derived from all three in-road sensors 64, 65, 66 to a central computer, or 15 retrieval in one of the various alternatives outlined above, is represented by step 8.23.
In-road sensor 66 is optional and is for system evaluation purposes. It is positioned between the electronic message sign 68 and the curve 62 and is used to monitor whether or not the message is heeded, i. e. , whether or not trucks are slowing down when instructed to do so by the message sign. The signals from its sensors are also 20 supplied to the programmable controller 69. This in-road sensor 66 need only supply information to enable truck speed to be determined and so comprises a truck axle sensor and a truck presence detector which is activated when a truck enters its field. The controller 69 processes the signals from in-road sensor 66 to produce a secondary truck record. As before, data from the controller 69 can be downloaded to a remote computer and truck records from the first in-road sensor and the second in-road sensor compared with the corresponding truck record from the third in-road sensor to determine the speed of the truck before and after the message sign. This allows statistics to be accumulated showing the number of trucks slowing down when instructed to do so by the message sign, thereby allowing evaluation of system effectiveness.

The system algorithm is site specific to accommodate certain site characteristics.
The software can be compiled on any curve site with a known camber and radius.
The data is stored on site in the programmable controller and is retrievable either by a laptop computer on site or remotely via modem communication. The controller also has an auto-calibration feature. If the system fails for any reason, an "alert"
signal is transmitted to the host computer via modem, informing the system operators of a system malfunction.
The programmable controller allows the system operator to adjust maximum allowable safe speeds, based on collected data on truck speeds at particular locations.
For example, if the maximum safe speed is set at the posted speed limit, but if the majority of trucks are exceeding the posted speed limit at a particular location, then the variable message warning sign would be excessively activated, and the system would lose its effectiveness. Therefore, it is desirable to adjust speed threshold parameters to increase system effectiveness. The centre of gravity for each truck is estimated from the rollover threshold tables.
As an option to the main classification and detection sensors, on-scale detectors may be incorporated into each lane to ensure that the trucks passing the sensor arrays are fully within the active zone of the system, and are not straddling a lane. The on-scale detectors effectively eliminate the possibility that a truck will receive a message for a speed that is higher than is safe for that particular truck.
The electronic message sign conveniently is installed directly below a traditional information sign (e.g., a "danger ahead" sign with the image of a truck rolling over) which indicates the ramp advisory speed. The message sign is not a continuous beacon which flashes continuously. Rather, it is a sign which is activated only when a truck is exceeding the rollover threshold speed at a particular curve. A message for a specific truck is more effective, since the sign is an exception to regular signing and not a common background feature.
(iii) VEHICLE RAMP ADVISORY SYSTEM
One embodiment of an aspect of this invention, the Vehicle Ramp Advisory System (VRAS), for detecting potential rollover of truck approaching a curve, will now be described with reference to FIGS. 9 through 11B. This embodiment of an aspect of this invention, namely the VRAS is an intelligent transportation system which helps prevent rollover accidents and out-of-control vehicles on sharp curves, e.g., freeway exit ramps. FIG. 9 shows the components of a VRAS traffic monitoring system which is deployed between an exit 90 of a highway 91 and a curved ramp 92 of the exit road 93.
The system comprises a first set of above-road electro-acoustic sensor arrays which are directed at the left hand lane of the exit road upstream of the curve 92, as station # 1 sensors. Above-road electro-acoustic sensor arrays 1711 F comprise a set of above-road electro-acoustic sensor arrays which are similar to those used in the aspect described in FIG. 1 to FIG. 5, and so need not be described further. A typical orientation thereof will, however, be described hereinafter in FIG. 18 to FIG.
21. The system also comprises a second set of above-road electro-acoustic sensor arrays 1711G
which are directed at the right hand lane of the exit road upstream of the curve 92, as station # 2 sensors. Since the operation is the same for both sets of above-road electro-acoustic sensor arrays, only the above-road electro-acoustic sensor arrays in the left hand lane will be described further. A traffic signal device, in the form of an electronic message sign 98, is disposed downstream from above-road electro-acoustic sensor arrays 1711F, and is associated with the left hand traffic lane, for example, above it or at an elevated height adjacent to it. The exit road has two lanes and hence a duplicate set of a traffic signal device 98A is provided for the right hand lane downstream from above-road electro-acoustic sensor arrays 1711G.
As an optional feature, the system may also comprises a third set of above-road electro-acoustic sensor arrays 1711H which are directed at the left hand lane of the exit road downstream from the first set of above-road electro-acoustic sensor arrays 1711 E, but upstream of the traffic signal device 98E, as station # 3 sensors. Above-road electro-acoustic sensor arrays 171 1H comprise electro-acoustic sensors which are similar to above-road electro-acoustic sensor arrays 1711F. In this optional feature, the system may also comprises a fourth set of above-road electro-acoustic sensor arrays 17111, which are directed at the right hand lane of the exit road downstream of the first set of above-road electro-acoustic sensor arrays 1711G but upstream of the traffic signal device 98F, as station # 4 sensors. Above-road electro-acoustic sensor arrays 17111 comprise above-road electro-acoustic sensor arrays which are similar to above-road electro-acoustic sensor arrays 1711G.
Referring now to FIG. 10, the station # 1 sensors (above-road electro-acoustic sensor arrays 1711F), the station # 2 sensors (above-road electro-acoustic sensor arrays 1711G), the station # 3 sensors (above-road electro-acoustic sensor arrays 1711 H), the station # 4 sensors (above-road electro-acoustic sensor arrays 17111) and the electronic message signs 68, 68A are connected to a roadside controller 99, 99B, which comprises the same basic components as the roadside controller of the aspect described in FIG. 1 to FIG. 5 above. The roadside controller 99 includes a microcomputer 99B, and a modem 70. The microcomputer 99B contains software and data for processing the sensor signals to give vehicle class based on vehicle length, number of axles and axle spacings, and vehicle speed. The microcomputer 99B is preprogrammed, upon installation, with site-specific data, e.g., camber and radius of the curve, and the various distances between the above-road electro-acoustic sensor arrays and the curve. In use, the processor uses the site-specific data, and the truck-specific data derived from the above-road electro-acoustic sensor arrays 1711F, 1711G, 1711H, 17111, to compute deceleration between the above-road electro-acoustic sensor arrays 1711F, 1711H, and above-road electro-acoustic sensor arrays 1711G, 17111 and to predict the speed at which the truck will be travelling when it arrives at the curve 92. Taking into account height and class of the truck, and camber and radius of the curve, the processor determines a maximum safe speed at which that particular class of truck should attempt to negotiate the curve. If the predicted speed exceeds this maximum, implying a risk of rollover occurring, the processor activates the message sign to display a warning, e.g., "TRUCK REDUCE
SPEED!" or some other suitable message. The sign is directional and is viewed only by the driver of the passing truck. The threshold speed is programmable and can be inputted or changed by the system user.
More specifically, in this aspect of this invention, the VRAS uses above-road electro-acoustic sensor arrays, which are known by the trade-mark SmartSonicTM, to detect vehicles and to classify them according to type by means of determination of the length of the truck and truck classification tables which are loaded into the computer.
All information from the above-road electro-acoustic sensor arrays is processed in real time, just milli-seconds after the vehicle has passed through the detection zone. If the speed of the vehicle (as determined by the above-road electro-acoustic sensor arrays) exceeds the posted advisory speed, and the vehicle is classified as a truck, a warning status is assigned to the vehicle. The warning status produces a trigger signal which activates the message sign. The message sign is only activated for vehicles which are assigned a warning status and is specific to that particular vehicle. Since the message signs are only activated for particular vehicles, they are more noticeable and are more likely to achieve the desired response of vehicle speed reduction.
The VRAS is meant to complement the existing static signing by providing a warning and drawing the attention of a driver to the fact that the safe speed has been exceeded and that the vehicle should slow down to avoid a potential rollover or accident resulting from a loss of control. It should be recognized that the accuracy of the system is dependent on site conditions and traffic flow characteristics.
While it is not desired to be limited to any particular type of message sign, in one non-limiting embodiment, the message signs are fibre optic message signs. The station #1 sensors, station #2 sensors, station #3 sensors, station #4 sensors, and electronic message signs are all interlocked, e.g., by suitable cables disposed within, e.g., a conduit 97 of 1/~" diameter. Typically, the distance between station #1 sensors 1711F
and electronic message sign 98F is 250 feet, and the distance between station #2 sensors 1711G and electronic message sign 98G is likewise 250 feet.
As will be further described with reference to FIG. 16, the above-road electro-acoustic sensor arrays are mounted on poles.
A truck entering the system passes through the detection zones of the above-road electro-acoustic sensor arrays. As noted above, the above-road electro-acoustic sensor arrays are mounted on poles and are aimed at specific areas on the roadway through which the traffic will pass. Since two lanes are to be equipped at this site, above-road electro-acoustic sensor arrays are installed on both shoulders. For each lane, two detection zones are used. The above-road electro-acoustic sensor arrays provide data which is processed by the controller electronics to determine inter alia vehicle speed.
If a warning status is assigned by the system, the roadside message signs will be activated for that particular vehicle. The message sign will remain on for a specified 5 period of time, until the vehicle has passed the roadside static sign. A
single controller is used to receive and process information from all of the above-road electro-acoustic sensor arrays plus control the operation of the message signs. The electronics are compact and therefore easy to mount on the same pole that is used to mount the sensors.
In one aspect of this invention, where only Station #1 and Station #2 above-road electro-10 acoustic sensor arrays are used, a timer will shut off the message sign based on the time the vehicle is detected and the vehicle speed.
While it is not desired to be limited to any particular class of message sign, one non-limiting example of such message sign is a fibre optics message sign. One such non-limiting example of the fibre optics message sign is a highly visible roadside message 15 sign to provide a real-time, eye-catching message to truck drivers. Such non-limiting example simple of a single message fibre optic message sign may be used to communicate clearly to the driver. For example, the fibre optic message sign may contain the message:
TRUCK

SPEED
While it is not desired to be limited to any particular manner of control of the illumination of the message sign, one non-limiting example of the control of the illumination of the sign is by electronics. When a warning message is necessary, the 25 system turns the message sign on so that the targeted driver sees the message. In one non-limiting example, the timing of the activation and duration of the activation of the message sign may be controlled to give optimum visibility and viewing time to the driver, while minimizing the possibility of a following driver viewing the sign in error.
While it is not desired to be limited to any particular intensity of the sign, one non-limiting example of the intensity of the illumination of the sign is one which has a minimum of two different and adjustable intensities for day and night light levels, ensuring good visibility. While it is not desired to be limited to any particular sign characters, in one non-limiting example, such sign characters may have a minimum height of 10" and may be readable from a distance of at least 500 feet under all lighting conditions.
While it is not desired to be limited to any particular structure of housing for the sign, one non-limiting example of the housing of the sign is an aluminum alloy with a minimum thickness of 0.125" . While it is not desired to be limited to any particular type of construction of housing for the sign, one non-limiting example of such housing is one in which all exterior seams may be welded and made smooth. In one non-limiting example, the entire housing may be made weatherproof. In one non-limiting example, a rubber seal or other approved seal material may be provided around the entire door to ensure a watertight enclosure.
While it is not desired to be limited to any particular structure of the fibre optic network of such fibre optic message sign, one non-limiting example of such fibre optic network may be one which consists of fibre optic bundles which are arranged to form the required letters. In such non-limiting example, each bundle may consist of a minimum of 600 fibres, ground smooth and polished at the input and output ends for maximum light transmission. In such non-limiting example, spare bundles numbering at least 5% of the total bundles are connected to each light source for future replacement of damaged bundles.
While it is not desired to be limited to any particular type of light source, one non-limiting example of the light source for each bundle may be from two 50 watt quartz halogen lamps with at least an average 6000 hour rated life. In such non-limiting example, a minimum of four bulbs may be provided for the entire message sign.
In such non-limiting example, no more than 50% of the illumination of each bundle may come from a single bulb. In such non-limiting example, in the event of the failure of a single bulb in a pair, the bundles continue to be illuminated at 50% of normal brightness. In such non-limiting example, alternating bundles in a message sign face may be connected to different light sources, such that a lamp failure will affect only alternating pixels.

In another embodiment, where Station # 3 and Station # 4 above-road electro-acoustic sensor arrays are used, these above-road electro-acoustic sensor arrays, which determine deceleration and predict speed, can be used to turn off the message sign based on that speed. In this aspect, therefore, the operation of the message signs is controlled by the vehicle speed.
The controller electronics passes the real time vehicle information to a micro-controller. All vehicle information is stored in the memory of the controller and is retrievable manually at the controller cabinet. Data which is collected by the system includes vehicle counts, vehicle speed, and vehicle length (according to classification groups). The microcontroller receives and processes vehicle information to make a decision on the message sign operation. If required, the controller activates and deactivates the real time warnings provided for drivers at the appropriate time.
The above-road electro-acoustic sensor arrays are used to provide vehicle speed information. The above-road electro-acoustic sensor arrays may be mounted on a pole at a height of approximately 20 feet just off the shoulder of the road as shown in FIG.
16. Each above-road electro-acoustic sensor arrays is directed at a particular area on the roadway. As will be described with reference to FIG. 18, a bank of microphones in the above-road electro-acoustic sensor arrays monitors the acoustic energy from the detection zone. The noise is filtered and analyzed to determine vehicle presence, type, and speed, as will be described with reference to FIG. 19 to FIG. 21.
The system operates as a vehicle advisory system by collecting vehicle speed and classification information. The passage of vehicles is monitored in real tinne, and determines whether the maximum safe entrance speed for that particular vehicle is exceeded. The system triggers the roadside message sign only if a vehicle is exceeding the posted maximum speed.
Raw vehicle records generally will include the following data, namely, site identification, time and date of passage, lane number, vehicle sequence number, vehicle speed, and code for invalid measurement.

The sequence of events for a vehicle record and message generation is outlined as follows:
1. Vehicle Data Collection:
The operation of the VRAS is triggered by a vehicle passing through the zones of the above-road electro-acoustic sensor arrays. When a vehicle passes through such detection zones, the system creates a new vehicle record to contain all of the information obtained for that vehicle. After passing through the detection zone, the controller processes the vehicle record to determine classification (length class) and speed.
2. Warning Status Determination:
2a. If the vehicle speed which was recorded during vehicle data collection is greater than the posted advisory speed, a warning status will be assigned specifically to that vehicle.
2b. If there is a second set of above-road electro-acoustic sensor arrays, such above-road electro-acoustic sensor arrays determine deceleration and calculate predicted speed.
3. Message sign activation:
If a warning status is assigned to the vehicle, the message sign will be activated.
As the vehicle continues along the roadway, the message sign will be deactivated according to a timer if the predicted speed is now below the posted advisory speed, or, according to Step 2a, if the actual speed is now below the posted advisory speed. Thus, the message sign will only be activated when necessary.
The sequence of operations as a vehicle is processed by the system will now be described with reference to FIG. 11A and FIG. 11B. When the vehicle passes under above-road electro-acoustic sensor arrays 1711F, the analysis of the sound determines whether the vehicle is a truck or is not a truck at step 11. 1. The processor determines, in step 11.2, whether or not a vehicle has been accurately detected. If it has not, step 11.3 records an error. If the vehicle has been detected accurately, and if no weigh-in-motion (WIM) scale is present, a typical weight and configuration of the truck is assumed. The microcomputer creates a truck record containing this information, namely, axle spacings and number of axles, length and electro-acoustic data, together with the time and date at step 11.4. If a weigh-in-motion (WIM) scale is present at 11.31, it uses information which is derived from the weigh-in-motion (WIM) scale, together with the time and date, to create a vehicle record. In decision step 11.5, from the information at steps 11.4 or 11.32, it compares the measurements with a table of vehicle classes to determine whether or not the vehicle is of a class listed, specifically one of various classes of truck. If it is not, the processor takes no further action as indicated in step 11.6. If decision step 11.5 determines that the vehicle is a truck, and that it was accurately detected, then, in step 11.14, the processor determines whether or not vehicle height is greater than a threshold value (e.g., eleven feet). If the vehicle height is greater than the threshold value, the processor proceeds to step 11.15 to identify it as a particular class of truck. If the height of the vehicle is less than the threshold value, steps 11. 15 and 11.16 identify the truck class and type.
Having identified the truck class and type in step 11.15 or in step 11.16, the processor proceeds to access its stored rollover threshold tables in step 11.17 to determine a threshold speed for that particular truck safely to negotiate the curve. In step 11.18, the measured speed at station # 1 is the speed of the truck when it arrives at the beginning of the curve 92. Step 11.19 compares the predicted speed with the rollover threshold speed. If the predicted speed is lower, no action is taken, as indicated by step 11.20. If the predicted speed is higher than the rollover threshold speed, however, step 11.21 activates the message sign 68 for the required period of time to warn the driver of the truck to slow down.
If the system does not include station #3 sensors, a timer determines, from the speed of the vehicle and the time lapse, when to deactivate the warning sign at step 11.2b.
If it is desired to provide deceleration calculations, the system may include station #3 above-road electro-acoustic sensor arrays, and the vehicle is detected by the above-road electro-acoustic sensor arrays at station #3 in step 11.22. The processor determines in step 11.23 whether or not a vehicle has been accurately detected. If it has not, step 11.34 records an error. If the vehicle has been detected accurately, the microcomputer creates a truck record of the speed together with the time and date at step 11.25. If such speed is lower than the rollover threshold speed, the timer sensed deactivation of the warning sign is overridden, but step 11.26 deactivates the message sign.
Step 11.27 represents the sequence of steps which are taken by the processor to process the corresponding signals from the above-road electro-acoustic sensor arrays 5 1711F and 1711G to ascertain the speed of the truck and the type of truck, and to create a secondary record. Subsequent transmission of the truck data which is derived from all three sensor arrays 64, 65, 66 to a central computer, or retrieval in one of the various alternatives outlined above, is represented by step 11.23.
The controller 99 processes the signals from all the electro-acoustic sensor arrays 10 to produce a secondary truck record. As before, data from the controller 99 can be downloaded to a remote computer and truck records from the first and third above-road electro-acoustic sensors compared to determine the speed of the truck before and after the message sign. This allows statistics to be accumulated showing the number of trucks slowing down when instructed to do so by the message sign, thereby allowing evaluation 15 of system effectiveness.
The system algorithm is site specific to accommodate certain site characteristics.
The software can be compiled on any curve site with a known camber and radius.
The data is stored on site in the programmable controller and is retrievable either by laptop computer on site or remotely via modem communication. The controller also has an 20 auto-calibration feature. If the system fails for any reason, an alert signal is transmitted to the host computer via modem, informing the system operators of a system malfunction.
The programmable controller allows the system operator to adjust maximum allowable safe speeds, based on collected data on truck speeds at particular locations.
25 For example, if the maximum safe speed is set at the posted speed limit, but if the majority of trucks are exceeding the posted speed limit at a particular location, then the variable message warning sign would be excessively activated, and the system would lose its effectiveness. Therefore, it is desirable to adjust speed threshold parameters to increase system effectiveness. The centre of gravity for each truck is estimated from the 30 rollover threshold tables.

As an option to the main classification and detection sensors, on-scale detectors may be incorporated into each lane to ensure that the trucks passing the sensor arrays are fully within the active zone of the system, and are not straddling a lane. The on-scale detectors effectively eliminate the possibility that a truck will receive a message for a speed that is higher than is safe for that particular truck.
The electronic message sign, namely, "TRUCK REDUCE SPEED !", conveniently is installed directly below a traditional information sign (e.g., a "danger ahead" sign with the image of a truck rolling over) which indicates the vehicle ramp advisory speed. The message sign is not a continuous beacon which flashes continuously. Rather, it is a sign which is activated only when a truck is exceeding the rollover threshold speed at a particular curve. A message for a specific truck is more effective, since the sign is an exception to regular signing and not a common background feature.
(iv) TRAFFIC SIGNAL PRE-EMPTION SYSTEM
A third aspect of this invention is a traffic signal pre-emption system, specifically a traffic signal pre-emption system which monitors truck speed at successive points along a steep downgrade to determine when there is a "runaway" truck and pre-empts traffic signals along the path of the runaway truck, will now be described with reference to FIG.

12 through to FIG. 15B.
The downhill speed warning system may be installed at the approach to a long, steep downhill grade, perhaps at the summit of a mountain pass. The downhill speed warning system comprises a system of above-road electro-acoustic sensor arrays and a programmable controller for classifying commercial vehicles, i.e. trucks, while they are in motion. Using that information and stored information which is specific to the downgrade, the system provides real-time safe descent speed calculations, and advises drivers of the safe descent speed by variable message signs, all before the truck begins to descend the downgrade. This embodiment may also be used in conjunction with hazards at other traffic-light-controlled intersections, or as a warning sign activator or preemptor at blind intersections.

FIG. 12 depicts a section through a steep downgrade 1202 with an intersection at the bottom. The intersection is controlled by traffic signals 1203 of conventional construction, i.e., the usual red, yellow and green lights, which are controlled by a traffic signal controller 1402 (FIG. 14). A truck 1201 is shown at the top of the downgrade. As the truck 1202 descends the downgrade, it will traverse a set of above-road electro-acoustic sensor arrays shown in more detail in FIG. 13. As in the other embodiments, a set of above-road electro-acoustic sensor arrays is provided for each traffic lane. A camera 1204, whose purpose will be described hereinafter, is also provided, as is a utilities box 1205.
Each set of above-road electro-acoustic sensor arrays, namely station # 1 sensors, comprise above-road electro-acoustic sensor arrays 1711J, 1711K, which are similar to those described previously, or in-road sensors, 1305A, 1306 1306A, and 1307, 1307A, which are spaced apart in the road surface along the downgrade. In-road sensors 1305, 1305A, 1306, 1306A, each comprise vehicle presence and direct axle detectors which are similar to those described previously, and are spaced 150 meters apart. In-road sensor 1307 is positioned 150 meters beyond the sensor array 1305 and comprises a vehicle presence detector and a direct axle sensor. Above-road electro-acoustic sensor arrays 1711 (namely, 1711J, 171 1K), or in-road sensors 1305, 1305A, 1306, 1306A and 1307, 1307A, are connected to a roadside controller 1408 similar to that of the other embodiments, including a processor and a modem 1409 (FIG. 14). As shown in FIG.
14, the roadside controller is connected to traffic signal controller 1401 which controls the sequence of the traffic signals 1402 and also a camera 1401 which is located adjacent the traffic signals.
As a vehicle traverses the zones of the above-road electro-acoustic sensor arrays, namely station #1 sensors, station #2 sensors and station #3 sensors, the processor determines the truck type, and the speed, using the signals from the above-road electro-acoustic sensor arrays 1711 (namely, 1711J, 1711K), or the in-road sensors 1105, 1306.
If the vehicle is a truck, using the preprogrammed site-specific data, including site characteristics, e.g., length and severity of the downgrade, the processor computes a maximum speed for that particular class of truck. From the signals from the above-road electro-acoustic sensor arrays 1711J, 1711K, or the in-road sensors 1306, 1306A, the processor determines whether or not the truck is exceeding the calculated maximum speed and whether the speed of the truck has increased significantly, or decreased, as determined either from above-road electro-acoustic sensor arrays 1711J, 1711K, or between the in-road sensors 1305, 1305A, 1306, 1306A. If the speed of the truck as it traverses the above-road electro-acoustic sensor arrays 1711K or the in-road sensors 1306, 1306A, is greater than the calculated maximum value, indicating that the truck cannot stop safely at the intersection, the processor transmits a pre-empt signal to the traffic signal controller 1401 which ensures that the traffic signals are in favour of the truck when it arrives at the intersection.
The specific sequence of operations is illustrated in FIG. 15A and 15B. On receipt of a signal from above-road electro-acoustic sensor arrays 1711 D, or from in-road sensors 1305, the processor determines, in steps 15.1 and 15.2, whether or not a truck has been accurately detected. If not, step 15.3 records an error. If the truck has been accurately detected, the processor processes the signals from above-road electro-acoustic sensor arrays 1711 (namely 1711J, 1711K), or signals from in-road sensors 1305, 1305A, 1306, 1306A, in step 15.4, to compute vehicle speed, bumper to bumper length, axle spacings and number of axles, measures or assumes the weight, and adds the time and date to the data before recording it. If the controller has problems processing any of the signals from the above-road electro-acoustic sensor arrays, or the in-road sensors a warning or error is added to the vehicle information to indicate that the calculated values may be in error. From the vehicle information, the processor uses stored data or "look-up" tables to determine vehicle type, based upon the length of the vehicle, the number of axles and the distance between each axle. From this classification, the processor determines, in decision step 15.5 whether or not the vehicle is a truck. If it is not, the processor takes no further action with the data, as indicated in step 15.6. If the vehicle data indicates that it is a truck, however, the processor computes, in step 15.7, a maximum safe speed for that truck based upon its configuration.
Upon receipt of a signal from the second above-road electro-acoustic sensor arrays 1711K or from in-road sensors 1306, 1306A, in step 15.8, the processor again determines whether or not the truck has been accurately detected (step 15.9).
If it has not, a truck error is recorded in step 15.10. If the controller has problems processing any of the signals from the above-road electro-acoustic sensor arrays, or from the in-road sensors, a warning or error is added to the truck information to indicate that the calculated values may be in error. If the truck has been accurately detected at the above-road electro-acoustic sensor arrays I711J, 1711K, or at sensor 96, the processor processes the signals from above-road electro-acoustic sensor arrays 1711J, 1711K, or from in-road sensors 1306, 1306A, in step 15.11 to determine the truck speed, bumper to bumper length, axle spacings and number of axles, and measures or assumes the weight. In step 15.12, it compares the actual truck speed measured at above-road electro-acoustic sensor arrays 1711K or at in-road sensors 1305, 1305A, with the actual truck speed which was measured at above-road electro-acoustic sensor arrays 1711J, or at in-road sensors 1306, 1306A. If the speed at sensor # 1 is greater than the speed at sensor # 2, the speed at sensor # 1 is used, at decision step 15.23. If the speed at sensor # 1 is not greater than the speed at sensor # 2, the speed at sensor # 2 is used, at decision step 15.22. The controller, by the use of the selected speed, obtains, from tables, a maximum stopping threshold for that truck classification. The stopping threshold will be based on standardized tables for each truck configuration.
When a signal is received from above-road electro-acoustic sensor arrays 1711J, 1711K or from in-road sensors 1306, 1306A, the processor again checks that the truck has been detected accurately (steps 15.14, 15.15) and records an error if it has not. If it has, in step 15.16 the processor processes the signals from above-road electro-acoustic sensor arrays 1711 to produce a record of to the truck speed, bumper to bumper length, axle spacings and number of axles, and measures or assumes the weight, and adds a time and date stamp as before. If the processor has problems processing any of the signals from the above-road electro-acoustic sensor arrays, or from the in-road sensors, a warning or error is added to the truck information to indicate that the calculated values may be in error. Based on the stopping threshold information determined in step 15.13, and the truck speed, as determined by above-road electro-acoustic sensor arrays 1711K, or the in-road sensors 1307, the processor will determine in step 15.17 whether or not the truck will be able to stop before the intersection if the traffic signal requires it. If decision step 15.17 indicates that it will be able to stop, the processor takes no further action as in step 15.18. However, if decision step 15.7 indicates that it will not be able to stop, the processor sends a signal to the traffic signal controller 100 as indicated in 5 step 15.19, causing it to pre-empt the traffic signal to keep the traffic flowing continuously in the direction the truck is travelling. The pre-emption signal will override the traffic signal sequence either to change the traffic signal to favour the passage of the vehicle or, if it is already in its favour, to ensure that the traffic signal does not change for a suitable interval. The duration of the traffic signal pre-emption is based upon site 10 specific geometrics and varies from site to site. The central controller can also be programmed to pre-empt the traffic signal as a precautionary measure when a warning or error occurs at any or all of the above-road electro-acous'tic sensor arrays 1711J, 1711K or the in-road sensors 1305, 1305A, 1306, 1306A, 1307 and 1307A.
As before, as an option to the main detection sensors, on-scale detectors may be 15 incorporated into each lane to ensure that the vehicles passing the sensor arrays are fully within the active zone of the system, and are not straddling a lane. The on-scale detectors effectively eliminate the possibility that a truck will receive a message for a speed that is higher than is safe for that particular truck.
It will be appreciated that there is potential for abuse, i.e., drivers deliberately 20 causing the system to pre-empt the traffic signals. Accordingly, whenever the traffic signal controller 1203 receives a pre-emption signal, it operates the roadside camera 1204, as indicated by step 15.20, to capture an image of the vehicle which caused the pre-emption signal. The video record will provide a means of identifying vehicles for safety and regulatory purposes.
25 As in the case of the other embodiments, all vehicle data collected from above-road electro-acoustic sensor arrays 1711 (namely, 1711J, 1711K), or from in-road sensors, (namely, 1305, 1305A, 1306, 1306A 1307 and 1307A) can be transmitted, via modem, to a central computer for analysis at step 15.21.
In any of the above-described aspects of this invention, the controller may be 30 reprogrammed with fresh data and table information, conveniently by means of, for example, a laptop computer. Moreover, instead of the data being transmitted via modem to the central computer, the data could be stored in the memory of the controller and retrieved periodically by, for example, a laptop computer. A remote terminal can be used to provide full remote control over the operation of the system, including controls, e. g. , disabling the system or overriding signal pre-emption where there is a false alarm.
An advantage of traffic monitoring systems embodying the present invention is that they perform real-time computations using information specific to a particular vehicle without necessarily knowing the weight of the vehicle and information specific to a particular potential hazard to determine what message, if any, to display to the driver of the vehicle or, in the case of the traffic signal pre-emption system, whether or not to pre-empt the regular traffic signal. Hence, the system reconunendations are tailored to the site and the specific vehicle. Consequently, there is less likelihood of erroneous or untimely messages being displayed and hence increased likelihood that drivers will heed the messages and/or not abuse the system.
In each aspect of this invention, the controller may also have an auto-calibration feature. If the system fails for any reason, an alert signal is transmitted to the host computer via modem, informing the system operators of a system malfunction.
The set of above-road electro-acoustic sensor arrays 1711, (namely 1711A, 1711B, 1711C, 1711D, 1711E, 1711F, 1711G, 1711H, 17111, 1711J and 1711K) are based on an improvement on a system which is used to monitor highway traffic, and will be described more fully hereinafter with reference to FIGS. 17 to 21.
(v) DESCRIPTION OF ELECfRO-ACOUSTIC SENSOR ARRAYS MOUNT
As seen in FIG. 16, the electro-acoustic sensor arrays 1711, designated 1601A
and 1601B, are mounted on a mast arm 1602. The mast arm 1602 is supported on a sensor mounting pole 1603, which includes a pole-mounted cabinet 1604. The pole-mounted cabinet houses the controller electronics of the above-road electro-acoustic sensors, known by the trade-mark SmartSonic,TM. The pole-mounted cabinet provides protection in a harsh outdoor environment, including protection from vandalism, rain, sleet, snow, dripping water, corrosion, hosedown, splashing water, and oil or coolant seepage. The sensor mounting pole 1604 is optionally provided with a breakaway base 1605. Beneath the roadway or the shoulder of the roadway is an electrical junction box 1606.
Typically the mast arm is 10 feet long, and the sensor mounting pole is 20 feet high. The above-road electro-acoustic sensor arrays are mounted on the poles and are aimed at specific areas on the roadway through which the traffic will pass.
Since two lanes are to be equipped at this site, above-road electro-acoustic sensor arrays are installed on both shoulders. For each lane, two detection zones are used. The above-road electro-acoustic sensor arrays provide data which is processed by the controller electronics to determine a vehicle speed.
(vi) ELECTRO-ACOUSTIC SENSORS
FIG. 17 to FIG. 21 will now explicitly describe the previously mentioned above-road electro-acoustic sensor arrays 1711, (namely 1711A, 1711B, 1711C, 1711D, 1711E, 1711F, 1711G, 1711H, 17111, 1711J and 1711K). Each motor vehicle using a highway radiates acoustic energy from the power plant (e.g., the engine block, pumps, fans, belts, etc.) and from its motion along the roadway (e.g., tire noise due to friction, wind flow noise, etc.). While the energy fills the frequency band from DC up to approximately 16KHz, there is a reliable presence of energy from 3KHz to 8KHz. Thus an analysis of such energy enables the classification of the vehicle as a truck or as not a truck.
FIG. 17 depicts an illustrative embodiment of an above-road electro-acoustic sensor array constituting an essential element of all of the systems of aspects of the present invention, which includes the monitoring of a predetermined area of roadway, called a "predetermined detection zone", for the presence of a motor vehicle and for the classification of such vehicle as a truck within that area. The salient items in FIG. 17 are roadway 1701, automobile 1703, truck 1705, detection zone 1707, microphone array 1711, microphone support 1709, detection circuit 1715 and interface circuit 1719 in a roadside cabinet (not shown), electrical bus 1713, electrical bus 1717 and lead 1721, which conducts a loop relay signal to a command centre.
A typical deployment geometry is shown in FIG. 17. In that particular geometry, the horizontal distance of the sensor from the nearest lane with traffic is assumed to be less than 15 feet. The vertical height above the road is advantageously between 20 and 35 feet, depending on performance requirements and available mounting facilities. It will be clear to those skilled in the art that the deployment geometry is flexible and can be modified for specific objectives. Furthermore, it will also be clear to those skilled in the art how to position and orient microphone arrays 1711 so that they are well suited to receive sounds from predetermined detection zone 1707.
Each omni-directional microphone in microphone array of the above-road electro-acoustic sensor arrays 1711 receives an acoustic signal which comprises the sound which is radiated, inter alia, from automobile 1703, or from truck 1705, and ambient noise.
Each microphone in microphone array 1711 then transforms its respective acoustic signal into an analog electric signal and outputs the analog electric signal on a distinct lead on electrical bus 1713 in ordinary fashion. The respective analog electric signals are then fed into detection circuit 1715.
To determine the presence or passage of a motor vehicle in predetermined detection zone 1707, the respective signals from the microphone array of the above-road electro-acoustic sensor arrays 1711 are processed in ordinary fashion to provide the sensory spatial discrimination needed to isolate sounds emanating from within predetermined detection zone 1707. The ability to control the spatial directivity of microphone arrays of the above-road electro-acoustic sensor arrays 1711 is called "beam-forming". It will be clear to those skilled in the art that electronically-controlled steerable beams can be used to form multiple detection zones. The analysis of the sounds which emanate from the predetermined detection zone 1707 broadly classifies a vehicle according to its length, the number of axles and the spacing of the axles, i.e., as a truck or not as a truck.
As shown in FIG. 18, microphone array of the above-road electro-acoustic sensor arrays 1711 preferably comprises a plurality of acoustic sensors 1801, 1803, 1805, 1807, 1809, 1811, 1813, 1815 and 1817, (e.g., omni-directional microphones), which are arranged in a geometrical arrangement known as a Mill's Cross. For information regarding Mill's Cross arrays, the interested reader is directed to Microwave Scanning Antenna, R.C. Hensen, Ed., Academic Press (1964), and Principals of Underwater Sound (3rd. Ed). R. J. Urick (1983). While microphone array 1711 could comprise "" CA 02655995 2009-02-24 only one microphone, the benefits of multiple microphones (to provide signal gain and directivity, whether in a fully or sparsely populated array or vector), will be clear to those skilled in the art. It will also be clear to those skilled in the art how to baffle microphone array 1711 mechanically so as to attenuate sounds coming from other than predetermined detection zone 1707 and to protect microphone array 1711 from the environment (e.g., rain, snow, wind, UV, etc.).
The microphone arrays of the above-road electro-acoustic sensor arrays 1711 are advantageously rigidly mounted on support 1709 so that the predetermined relative spatial positionings of the individual microphones are maintained. The microphone arrays of the above-road electro-acoustic sensor arrays 1711 may (as previously indicated) include a set of microphone arrays which are mounted on a mast arm which is supported on a pole, and another set of microphone arrays which are mounted the pole itself.
Alternatively, the sets of microphone arrays may be mounted on a highway overpass.
The height above the road may be 20 to 35 feet to aim at a point of up to 25 feet. The detection zone typically may cover an area of 4 to 8 feet by 6 to 12 feet.
(vii) DETECTION CIRCUIT
Referring to now to FIG. 19, detection circuit 1715 (See FIG. 17) advantageously comprises bus 1713, (See FIG. 17) bus 1901, vertical summer 1905, analog-to-digital converter 1913, finite-impulse-response (FIR) filter 1917, bus 1903, horizontal summer 1907, analog-to-digital converter 1915, finite-impulse-response (FIR) filter 1919, common multiplier 1921 and common comparator 1925. The electric signals from microphone 1801, microphone 1803, microphone 1805, microphone 1807 and microphone 1809 (as shown in FIG. 18) are fed, via bus 1901, into vertical summer 1905 which adds them in well-known fashion and feeds the sum into analog-to-digital converter 1913. While in the illustrative embodiment, vertical summer 1905 performs an unweighed addition of the respective signals, it will be clear to those skilled in the art that vertical summer 1905 can alternatively perform a weighted addition of the respective signals so as to shape and steer the formed beam (ie., to change the position of predetermined detection zone 1707). It will also be clear to those skilled in the art that illustrative embodiments of the above-road electro-acoustic sensor arrays providing systems constituting essential elements of the present invention can comprise two or more detection circuits, so that one microphone array can gather the data for two or more detection zones, in each lane or in different lanes.
Analog-to-digital converter 1913 receives the output of vertical summer 1905 and 5 samples it at 32,000 samples per second in well-known fashion. The output of analog-to-digital converter 1913 is fed into finite-impulse response filter 1917.
Finite-impulse response filter 1917 is preferably a bandpass filter with a lower passband edge of 4KHz, an upper passband edge of 6KHz and a stopband rejection level of 60dB below the passband (i.e., stopband levels providing 60dB of rejection). It will 10 be clear to those skilled in the art how to make and use finite-impulse-response filter 317.
The electric signals from microphone 1811, microphone 1813, microphone 1805, microphone 1815 and microphone 1817 (as shown in FIG. 18) are fed, via bus 1903, into horizontal summer 1907 which adds them in well-known fashion and feeds the sum into analog-to-digital converter 1915. While in the illustrative embodiments, horizontal 15 summer 1907 performs an unweighed addition of the respective signals, it will be clear to those skilled in the art that horizontal summer 1907 can alternatively perform a weighted addition of the respective signals so as to shape and steer the formed beam (i.e., to change the position of predetermined detection zone 1707). It will also be clear to those skilled in the art that illustrative embodiments of the above-road electro-acoustic 20 sensor arrays providing systems constituting essential elements of the present invention can comprise two or more detection circuits, so that one microphone array can gather the data for two or more detection zones, in each lane or in different lanes.
Analog-to-digital converter 1915 receives the output of horizontal summer 1905, and samples it at 32,000 samples per second in well-known fashion. The output of 25 analog-to-digital converter 1913 is fed into finite-impulse response filter 1919.
Finite-impulse response filter 1919 is preferably a bandpass filter with a lower passband edge of 4KHz, an upper passband edge of 6KHz and a stopband rejection level of 60dB below the passband (i.e., stopband levels providing 60dB of rejection). It will be clear to those skiIled in the art how to make and use finite-impulse-response filter 30 1919.

Multiplier 1921 receives, as input, the output of finite-impulse-response filter 317 and finite-response-filter 1919 and performs a sample-by-sample multiplication of the respective inputs and then performs a coherent averaging of the respective products. The output of multiplier 1921 is fed into comparator 1925. It will be clear to those skilled in the art how to make and use multiplier 1921.
Comparator 1925 advantageously, on a sample-by-sample basis, compares the magnitude of each sample to a predetermined threshold and creates a binary signal which indicates whether a motor vehicle is within predetermined detection zone 1707.
While the predetermined threshold can be a constant, it will be clear to those skilled in the art that the predetermined threshold can be adaptable to various weather conditions and/or other environmental conditions which can change over time. The output of comparator 1925 is fed into interface circuitry 1719.
Interface circuitry 1719 receives the output of detection circuitry 1715 and preferably creates an output signal such that the output signal is asserted when a motor vehicle is within predetermined detection zone 1707 and such that the output signal is retracted when there is not motor vehicle within the predetermined detection zone 107.
Interface circuitry 1719 also makes any electrical conversions necessary to interface to the circuitry at the command centre of the highway department. Interface circuitry 119 can also perform statistical analysis on the output of detection circuitry 1715 so as to output a signal which has other characteristics than those described above.
(viii) MAXIMALLY-DIGITAL IMPLEMENTATION
FIG. 20 illustrates a practical, maximally-digital, implementation. The microphone array 2000 comprises two vertical elements V, and V2, and two horizontal elements H, and H2. As shown, each element has three microphones, which was found practically sufficient. Each of the four elements V,, V2, H, and H2 feeds a respective analog filter 2001 to 2004 to attenuate unwanted noise outside the maximal frequency band of interest, which is normally between 4 and 9 kHz. The filters 2001 to 2004 are each followed by a respective selectable gain pre-amplifier 2005 to 2008, the gain of which is selectable in 3-Db steps ranging from 0dB to 15dB (hereinafter to be described more fully Iater). Four respective analog-to-digital converters 2009 to 2012 follow the pre-amplifiers 2005 to 2008. Respective digital finite impulse response (FIR) filters 2013 to 2016 follow the A/D convertors 2009 to 2012. The FIR filters 2013 to 2016 determine the actual frequency band of operation, which is selected from the following four bands:
Band 1: 4-6 Khz;
Band 2 : 5-7 Khz;
Band 3 : 6-8 Khz; and Band 4 : 7-9 Khz.

One value for the gain of all of the pre-amplifiers 2005 to 2008 will normally be selected for the four above bands as follows:
Band 1 Band 2 Band 3 Band 4 9dB 11dB 13dB 15dB
6dB 8dB 10dB 12dB
3dB 5dB 7dB 9dB
0dB 2dB 4dB 6dB
The selection of the frequency band would normally depend on the general nature of the expected vehicle traffic at the particular location of the sensor. The selected gain would depend, in addition, on the distance of the sensor from the road surface. The outputs of the FIR filters 2013 and 2014 (the paths of V, and Vz) are summed in digital summer 2017, while the outputs of FIR filters 2015 and 2016 (the paths of H, and H2) are summed in digital summers 2017 and 2018. The respective digital summers and 2018 are followed by digital limiters 2019 and 2020, respectively, and the outputs of the latter are input to correlator 2021, the output of which is fed to a parallel-to-serial convertor 2022, the serial output of which would normally be fed to a TDMA
multiplexer (TMDA-MUX) 2023 to be time-division multiplexed with other (conveniently four) processed microphone array signals originating from overhead locations near the array 2000. The multiplexed output of the TMDA-MUX 2023 is then normally relayed by cable 2024 to roadside microprocessor-based controller 2025, where it is demultiplexed in DEMUX 2026 into the original number of serial outputs representing the serial outputs of correlators, e.g., 2021. After demultiplexing in DEMUX
2026, the cross-correlated digital output from the correlator 2021 is integrated in integrator 2027 (which could be a software routine in the microprocessor/controller 2025), and, depending on the correlated/integrated signal level, which is compared to a threshold in vehicle detector 2028, a "vehicle present" signal is issued for the duration above threshold. This information is processed by a flow parameter calculation routine 2029 of the controller 2025, the output of which is an RS232 standard in addition to hard-wired vehicle presence circuits or relays (not shown).
(ix) OPERATION OF CONTROLLER
The operation of the controller 2025, whereby the demultiplexed signal from DEMUX 2026 is processed, will be better explained by reference to the flow-chart shown in FIG. 21. The signal is adjusted in gain/offset 2100 depending on user-specific parameters 2101 and then sampled at 2102 and integrated at 2103. The signal sampling 2103 continues until enough samples at 2104 have been collected, upon which the integrator 2103 is reset at 2105 and the mode is determined at 2106. If the mode is initially to indicate vehicle presence, and a vehicle is detected at 2107, which by sound analysis as hereinbefore described, classifies the vehicle as a truck, the decision is immediately outputted at 2107. If the mode 2106 is "free flow", then long term speed average is calculated at 2109 from which variable thresholds are progressively calculated at 2110. That is, the more vehicles there are, the more accurate will the average progressively become. This variable threshold is used to continue to determine vehicle presence at 2111, and to calculate flow parameters 2112. For example, from the average speed and the time the vehicle is in the detection zone, the length of the vehicle is determined, and the truck classification is confirmed. This progressively yields a better determination of the speed of the particular vehicle, given the length of the detection zone. The latter, of course, depends on the frequency band and the distance of the microphone array 2000 from the road surface. On average, in many applications, the length of the detection zone 1707 would be approximately six feet. The flow parameters 2112 are stored in memory 2113 and outputted at 2114 over the RS232 serial link to (other) central traffic management systems (not shown), and where desired activate other interface circuits. As may be seen, the "free flow" processing is iterative in nature, while the binary vehicle presence decision 2106 is determined by a user selected fixed threshold 2108.

Claims (3)

1. A method for providing traffic volume, line occupancy, per vehicle speed and vehicle classification of vehicles travelling along a highway, the method comprising::
receiving acoustic signals created and radiated by said vehicles as they travel through a detection zone; and signal processing said acoustic signals;
thereby to provide said traffic volume, line occupancy, per vehicle speed and classification of vehicles.

2. The method as claimed in claim 1, including the step of using advanced signal and spatial processing to provide adaptive interference cancellation and high resolution multi-lane or multi-zone traffic monitoring, including shoulder activity.

3. The method as claimed in claim 1 or claim 2, wherein said acoustic signals are received by means of non-contact, passive acoustic (listen only) above-road electro-acoustic sensor arrays which are mounted on overhead or roadside structures.