GPS-based traffic control preemption system

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FIELD OF THE INVENTION

This invention relates to a traffic preemption system and, more particularly, to a preemption system that receives data from a global positioning system (GPS) to track the approach of a vehicle requesting preemption of a traffic signal.

BACKGROUND

Traffic signals have long been used to regulate the flow of traffic. Generally, traffic signals have relied on timers or vehicle sensors to determine when to change the phase of traffic signal lights, thereby signaling alternating directions of traffic to stop, and others to proceed.

Emergency vehicles, such as police cars, fire trucks and ambulances, are generally permitted to cross an intersection against a traffic signal. Emergency vehicles have typically depended on horns, sirens and flashing lights to alert other drivers approaching the intersection that an emergency vehicle intends to cross the intersection. However, due to hearing impairment, road noise, air conditioning, audio systems and other distractions, a driver of a vehicle approaching an intersection will often not be aware of the warning signal being emitted by an approaching emergency vehicle, thus resulting in a dangerous situation.

This problem was addressed in the commonly assigned U.S. Pat. No. 3,550,078 to Long, which is incorporated herein by reference. The Long patent discloses that as an emergency vehicle approaches an intersection, the emergency vehicle emits a preemption request comprised of a stream of light pulses occurring at a predetermined repetition rate. A photocell, which is part of a detector channel, receives the stream of light pulses emitted by the approaching emergency vehicle. An output of the detector channel is processed by a phase selector, which then issues a phase request to a traffic signal controller to change or hold green the traffic signal light that controls the emergency vehicle's approach to the intersection.

While the system disclosed by Long proved to be a commercial success, it became apparent that the system did not have adequate signal discrimination. In addition, the length of time during which the pulse request signal remained active after the termination of light pulses was not uniform and sometimes too short to allow safe transit of the emergency vehicle.

Commonly assigned U.S. Pat. No. 3,831,039 (Henschel), which is incorporated herein by reference, improves on the system disclosed in the Long patent by improved selectivity of low repetition rate light sources of gas discharge lamps, such as fluorescent lights, neon signs, and mercury vapor lights. Further, Henschel improves the discrimination between a series of equally spaced light pulses and a series of irregularly spaced light pulses such as lightning flashes.

In the system disclosed by Henschel, the stream of light pulses must have proper pulse separation and continue for a predetermined period of time. Also, once a preemption call is issued to the traffic signal controller, the preemption call must remain active for at least a predetermined time period. The discrimination circuit disclosed by Henschel provides an improvement over the discrimination circuit disclosed by Long and results in improved discrimination.

Although such systems contemplated that preemption systems would be used for emergency vehicles, it was desirable to use them with non-emergency vehicles such as buses and maintenance vehicles. It thus became necessary to differentiate between different types of emergency and non-emergency vehicles. The commonly assigned U.S. Pat. Nos. 4,162,477 (Munkberg) and 4,230,992 (Munkberg), which are incorporated herein by reference, disclose an optical traffic preemption system wherein different vehicles transmit preemption requests having different priority levels, and in which the signal controller can discriminate between requests of differing priority and give precedence to the higher priority signal. The optical emitter disclosed by Munkberg transmits light pulses at a variety of selected predetermined repetition rates, with the selected repetition rate indicative of a priority level.

Commonly assigned U.S. Pat. No. 4,734,881 (Klein and Oran) which is incorporated herein by reference, provides for performance of the optical preemption functions with logic based circuity replacing a large number of discrete and dedicated circuits. The microprocessor circuitry utilizes a windowing algorithm to validate that pulses of light were transmitted from a valid optical traffic preemption system emitter.

Commonly assigned U.S. Pat. No. 5,172,113 (Hamer) which is incorporated herein by reference, discloses a method of optically transmitting data from an optical emitter to a detector mounted along a traffic route used specifically to receive data or to an optical traffic preemption system located at an intersection. Hamer allows variable data to be transmitted in a stream of light pulses by interleaving data pulses between priority pulses. For example, an emergency vehicle can transmit data in a stream of light pulses from an optical emitter that can include an identification code that uniquely identifies the emitter, an offset code that causes a phase selector to create a traffic signal timing cycle offset, and an operation code that causes traffic signal lights to assume at least one phase. Further, an emitter can transmit setup information, for example a range setting code that causes a phase selector to set a threshold to which future optical transmissions will be compared. Phase selectors constructed in accordance with the Hamer disclosure are provided with a discrimination algorithm which is able to track a plurality of optical transmissions with each detector channel. Optical emitters as disclosed by Hamer are provided with a coincidence avoidance mechanism which causes overlapping optical transmission from separate optical emitters to drift apart. Hamer discloses an optical signal format that allows variable data to be transmitted, while maintaining compatibility with existing optical traffic preemption systems.

One problem with all of the above described optical systems is that they require a line-of-sight to the signal controller at the intersection due to the optical nature of the preemption signal. Thus, while they may work acceptably for road systems which follow a rectangular grid pattern, they suffer several disadvantages. For example, where approaches to an intersection are blocked from line-of-sight or follow an irregular, curved or abruptly angled pattern, optically-based systems are not effective because they require a line of sight to the receiver.

Radio based, as opposed to optically based systems, for traffic control preemption have also been developed. For example, U.S. Pat. No. 2,355,607 (Shepherd) describes radio communications systems for vehicular traffic control wherein a directional transmission and/or reception located at the intersection, or on the vehicle, provides traffic light control based on coded signals transmitted from emergency vehicles. However, the inherent lack of directional precision of the radio system causes numerous traffic lights positioned parallel to the direction of travel to be affected. This is a major disadvantage because such prior art radio transmitter systems may erroneously pre-empt signal lights which are not on the approach route of an on-coming vehicle demanding preemption.

Radio transmitter systems also suffer from range inaccuracies which may be caused by signal attenuation or reflection. For example, a building may block, reflect, or attenuate a radio frequency which is not a line-of-sight signal. Since radio transmitter systems typically use signal strength to estimate range, signal attenuation gives rise to inaccurate range estimates at the receiving intersection electronics. Adverse weather, such as precipitation or fog, may also adversely affect the range sensitivity of existing radio transmitter dependent systems.

Efforts to reinforce radio systems with additional control functions are disclosed in U.S. Pat. No. 4,443,783 (Mitchell) wherein a directional transmitter is located in the approaching vehicle with omnidirectional receivers at intersections and multiple frequencies, selected frequency combinations, and selected red and amber light combinations provide accommodation for inaccuracies. U.S. Pat. No. 4,573,049 (Orbeck) discloses two way communication of information on intersection preemption request and action.

A major drawback of radio transmitters is that while they do not require a line-of-sight approach, their inherent lack of directionality means that they may erroneously control a signal light which is not on the vehicle's route but which is proximate the route.

There is therefor a need for a traffic preemption system for locations where approaches to an intersection are not line-of-sight or where road systems do not follow a rectangular grid pattern. Such a system would desirably offer the following advantages: (1) discretion without the need for a strobe as used in optical systems; (2) immunity from weather effects on system range; and (3) capability for easy implementation in applications with curving or abruptly angled approaches.

SUMMARY

The present preemption system provides a traffic control preemption system using data received from a global positioning system (GPS). GPS signals are received and processed by a GPS receiver and a processor module in the vehicle to generate navigational vehicle data, such as position, heading and velocity. The vehicle data, along with other data such as vehicle identification codes, priority codes or a preemption request, are transmitted via radio waves or some other medium. Each intersection is equipped with an intersection module adapted to receive and process the vehicle data. Each intersection module contains a preprogrammed map of allowed approaches to the intersection. Each intersection module within range of a vehicles transmitting equipment compares the received vehicle data with the map of allowed approaches. If the vehicle data sufficiently matches the map of allowed approaches to a particular intersection, the intersection module forwards the vehicle's preemption request to the intersection controller.

The present preemption system also preferably includes speed and heading sensors which provide vehicle data in areas of GPS signal obstruction or multipath. The system also provides multiple priority levels for different types of vehicles requesting preemption. In addition to traffic signal preemption, the system may also be used to provide for automatic vehicle location information for scheduling or traffic flow control purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects, features, and advantages of the present preemption system will become apparent upon reading and understanding the following detailed description and accompanying drawings in which:

FIG. 1 shows a system level block diagram of a first embodiment of the present traffic control preemption system;

FIG. 2 shows a system level block diagram of an alternate embodiment of the present traffic control preemption system;

FIG. 3 shows a system level block diagram of an additional alternate preferred embodiment;

FIG. 4 shows a schematic roadway diagram illustrating operation of the traffic control preemption systems of FIGS. 1 and 2;

FIG. 5 shows a schematic roadway diagram illustrating operation of the traffic control preemption system of FIG. 3;

FIG. 6 shows a schematic roadway illustrating operation of the present preemption system in a GPS obstruction or multipath zone;

FIG. 7 shows the control flow of absolute position mapping of the preemption system of FIGS. 1 and 2;

FIG. 8 shows the control flow for relative position mapping of the preemption system of FIG. 3; and

FIG. 9 shows the control flow for tracking of vehicle position to determine whether a vehicle is in the allowed preemption corridor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a system level block diagram of a preferred embodiment of the present GPS-based traffic control preemption system. The present preemption system utilizes information received from a global positioning system (GPS) 5 to determine whether a particular vehicle is within an allowed approach of an intersection. The GPS 5 is well known and has many defense and civillian uses. The GPS 5 is a space-based radio navigation system maintained by the U.S. Department of Defense, and consists of a constellation of 18 or more orbiting satellites. From these satellites, any user equipped with appropriate GPS receivers can determine their position anywhere in the world to within .+-.100 meters. Error purposely induced into the system by the U.S. Department of Defense limits the accuracy of the GPS for civillian use to .+-.100 meters. This GPS induced error varies over time. More detail regarding the GPS can be found in the article, "The Global Positioning System", by Ivan A. Getting, IEEE Spectrum, pp. 36-37, December 1993.

The preemption system of FIG. 1 also comprises a vehicle module 100 and an intersection module 200. The GPS signal 10 is received by GPS receiver antenna 20 and transmitted to GPS receiver 40, which is available from Rockwell International Corporation, Richardson, Tex., as Rockwell Corporation Model NAVCORE V.TM.. The GPS receiver 40 processes the GPS signal 10 to determine various navigational data regarding the vehicle, such as the vehicle's position, heading and velocity.

The vehicle position can be measured and processed by the present vehicle module 100 and intersection module 200 by any one of many known navigational coordinate systems. For example, the World Geodetic System (WGS-84) measures position in terms of latitude and longitude. The Earth-Centered, Earth-Fixed (ECEF) system is a spherical coordinate system with its origin at the center of the earth. It shall be understood that position may be measured in these or any other coordinate systems without departing from the scope of the present invention.

In addition to the navigational data regarding the vehicle such as position and heading, the GPS receiver 40 also generates information regarding which set of GPS satellites were used to determine the navigational data. Other data regarding the vehicle, such as priority codes, mode commands, identification codes and traffic control preemption request may also be generated as appropriate by processor 60.

All of the data generated by GPS receiver 40 and by processor 60 (hereinafter referred to collectively as "vehicle data") is then transmitted via transmitter 80 and antenna 101 to the intersection module 200. Intersection module 200 includes a data receiving antenna 210 which receives the vehicle data from the vehicle transmitting antenna 101. The vehicle data is then transmitted to a data receiver 230, which converts the radio frequency signal to digital form and outputs the vehicle data to a processor 250. The receiver antenna 210, receiver 230, transmitter antenna 201 and transmitter 80 are available as Modpak Plus Wireless Modem.TM., available from Curry Controls Company, Lakeland, Fla.

Each intersection includes an intersection controller 320, which controls the phase of traffic signals at the intersection, allowing alternating directions of traffic to proceed or stop. Such intersection controllers are well-known in the art. Each intersection controller thus controls the traffic signal for all possible approaches to a particular intersection. At a 4-way intersection, vehicles may approach from the north, south, east or west, for example. However, in a radio-based system, preemption requests from all of the allowed approaches, and even those on approaches belonging to different intersections (within range of the receiver antenna 210), are received by the intersection controller. The present preemption system therefor determines whether a vehicle is within one of the allowed approaches to that intersection. In order to properly control the phase of