Communications: electrical – Override of traffic control indicator by command transmitter
Reexamination Certificate
1999-11-03
2001-06-05
Trieu, Van T. (Department: 3632)
Communications: electrical
Override of traffic control indicator by command transmitter
C340S907000, C340S988000, C701S201000, C701S213000
Reexamination Certificate
active
06243026
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to GPS and traffic preemption.
BACKGROUND OF THE INVENTION
This invention relates generally to control of traffic signals under emergency conditions and, more particularly, to systems for automatic control of traffic signals in such a way as to preempt normal signal operation and permit the unimpeded and safe passage of emergency vehicles, such as ambulances, police cars, fire trucks and so forth. Without preemption, drivers of emergency vehicles often find themselves stuck in congested traffic or are forced into dangerous traffic maneuvers. These include entering opposing traffic lanes and running red lights. The latter is particularly dangerous, since a motorist who has the green may not see the approaching emergency vehicle until it is too late. There is a related need for preemption control systems to give priority to non-emergency vehicles, such as buses, which have to maintain a schedule in busy traffic. It has been widely accepted that, particularly in high density traffic areas, there is a vital need for such systems. Not only must an emergency vehicle be free to move through an intersection in a selected direction of travel, but the traffic flow in other directions, which could interfere with the movement of the emergency vehicle, must be stopped by an appropriate signal indication until the emergency vehicle has passed.
A number of present day systems have been utilized to accomplish this general purpose, but all have fallen short of the desired result in some respect. A common approach has been to provide apparatus on the emergency vehicle to transmit an emergency signal to a receiver associated with the traffic signal. The traffic signal controller, which has been suitably modified, is actuated to operate the signals in a predetermined emergency sequence. Some systems of this type require the installation of a receiver or sensor under the road surface, to detect where the vehicle is located with respect to the traffic signals. Obviously, systems of this type present difficulties of installation and maintenance. Various traffic preemption systems use radio signals, infrared signals, ultrasonic signals, audio signals or optical signals transmitted from the emergency vehicle and detected in some manner at the controlled intersection. A common difficulty with all systems of the prior art is that of accurately determining the time of arrival of the vehicle at the intersection. Clearly, preemption of normal traffic control should not occur too early. Apart from the obvious inefficiency this entails, there is an element of risk in that impatient drivers may try to enter a controlled intersection before the emergency vehicle arrives. Various techniques have been proposed for determining vehicle location and estimating arrival time. For example, electronic “signposts” can be installed beside or beneath the roadway to detect the passage of vehicles. Such systems are used, for example, to determine the locations and predicted arrival times of buses and to help maintain more accurate bus schedules. For the traffic preemption problem, however, installing multiple sensors or “signposts” near each intersection would be very expensive and still would not necessarily provide the desired accuracy.
More specifically, optical preemption systems are limited by the line of sight between the vehicle and the intersection control unit. Audio preemption systems detect the sound of an approaching siren on an emergency vehicle and take appropriate action. Unfortunately, the sound can be blocked by other vehicles or buildings, and microphones must be installed at points approaching the intersection.
Radio preemption systems currently available utilize signal strength to determine distance from the intersection. However, natural variations in terrain and man-made obstructions render this approach quite inaccurate.
Beacon based systems are more accurate, but do not permit subsequent adjustment to preemption distance needed for changing traffic patterns or construction zones. Also the installation cost of a beacon system is high because long lengths of underground cable has to be installed beneath the intersection and its approaches. Sensor loops underground are used to sense the vehicle positions, but are prone to breakage in cold weather. A failed sensor can render the system inoperative while repairs are made over an extended period, possibly months.
Another common aspect of traffic signal preemption systems is that they are typically manually actuated from the emergency vehicle. When the driver actuates a button or switch in the vehicle, an emergency signal is transmitted to the controller at the intersection, to preempt normal operation and modify the controller temporarily for passage of the vehicle. Some systems allow the driver to indicate a direction of turn at the intersection, so that the traffic signals can be appropriately controlled during preemption. However, existing preemption systems are typically not optimized to disrupt normal traffic control for as short a time as possible, or to clear as much of the interfering traffic as possible from the intersection. Moreover, existing preemption systems have no provision for preempting signals at adjacent intersections to one side or the other of the vehicle direction of travel when a preemption request is made. In existing systems, some intersections may not be preempted soon enough, if the vehicle deviates from a straight path along a single street, and may be preempted unnecessarily if the vehicle turns before reaching a nearby preempted intersection. The present invention has the goal of providing safe and unobstructed passage for emergency vehicles, while at the same time minimizing disruption of normal traffic through the intersection, and eliminating many of the disadvantages of the prior art systems.
SUMMARY OF THE INVENTION
The present invention resides in a traffic signal preemption system using differential global positioning system (GPS) measurements, and a related method of operation of the system. The present traffic preemption system and method provides green traffic signals to emergency vehicles while minimizing disruption of normal traffic flow. This provides the basic goal of facilitating travel of emergency vehicles, while reducing the undesirable effects. It will save lives and property in fewer traffic accidents and in reduced legal liability.
The system and method works in all weather and reliably handles complex road networks, including closely spaced intersections, curves and corners.
The system and method uses GPS to determine vehicle position, direction of travel, speed and time of day.
Also, the present system and method keeps preemption in effect for a minimized period so that a motorist who is held at a lengthened red light will not conclude that the lights are faulty or become impatient and run the red light.
In the present system and method, a single vehicle can preempt a whole series of intersections, so that the driver sees nothing but green lights along the emergency route. This includes curved roads, sharp turns, intersections with “dog-ear” approaches, and complex road networks which do not follow any kind of grid. Each signal is preempted at the optimum time depending on vehicle speed, with preemption occurring sooner (at a greater distance) as speed increases. Signals can also be preempted around comers, since the preemption system and method will respond to turn signals of emergency vehicles.
Briefly, and in general terms, the system of the invention includes a traffic signal subsystem and a vehicle subsystem. The traffic signal subsystem includes a GPS reference receiver having an antenna installed at a known position, for receiving GPS signals and computing measurement corrections for the GPS signals, a traffic signal controller capable of operation in a normal mode, and in a preemption mode when an emergency vehicle approaches the intersection, a communication radio for receiving data from an approaching emergency or other vehicle, and an intersectio
Beck James C.
Jones Gary V.
Judge Kevin
Keegan Richard
3M Innovative Properties Company
Olson Peter L.
Trieu Van T.
LandOfFree
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