Abstract:
System and method for the improved operation of a traffic signal system which reduces delays to vehicular traffic at one or more signalized intersections by detecting vehicular demand for movement through each intersection. The present invention uses detectors for detecting vehicles entering an intersection, at a distance sufficiently great from the intersection, and for detecting vehicles leaving an intersection, at a distance sufficiently near to the intersection, to permit, when possible, one or more vehicles to proceed completely through the intersection prior to coming to a near, or complete stop. The system and method further facilitates accident reduction by monitoring portions of traffic lanes entering an intersection for vehicles, determining the probability of a vehicle being able to timely stop for a halt signal, and, if it is determined that the vehicle cannot timely stop for a halt signal, attempting to clear the intersection of other vehicles by setting all signals to halt.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system and method for the improved operation of a traffic signal system which reduces delays to vehicular traffic at one or more signalized intersections by detecting a vehicle&#39;s demand for movement through each intersection, and, when possible, permitting the vehicle to proceed through one or more intersections, prior to the vehicle coming to a near, or complete, stop and/or which facilitates accident reduction by monitoring portions of traffic lanes entering an intersection for vehicles, determining the probability of a vehicle being able to timely stop for a halt signal, and, if necessary, attempting to clear the intersection of other vehicles. 
     DESCRIPTION OF THE RELATED ART 
     Traffic signals are commonly used to control and facilitate the orderly progression of vehicles through intersections. Early traffic signals were operated by traffic officers using manual switches to activate signal displays at intersections. To automate these signals and improve intersection efficiency, controller units for controlling the traffic signals were developed and implemented. The basic function of these early controller units was to alternately assign the right-of-way between two or more traffic lanes with conflicting traffic movements. 
     These early controller units were electromechanical pre-timed devices, using motors and gears for timing, that could change the signal displays. These early controllers, however, were not easily adjustable and repeated cycle after cycle for each lane of traffic on one or more pre-set timing plans, without regard to actual vehicle demand. Although the cycle timing could be adjusted to accommodate the needs of periodic heavy movement, such as morning and evening peaks, these controllers could not cope with, nor could they provide flexibility for, the changes in traffic flow that occurred throughout the day. This inflexibility often meant that a signal was showing stop for vehicles in a traffic lane that needed to proceed through the intersection, and vice versa. 
     The development of traffic actuated controller units provided some flexibility for accommodating varied traffic flow. These actuated traffic controller units permitted cycle timing to be varied for some or all controlled conflicting traffic lanes (i.e., lanes of traffic that would have interfering vehicle movements through the intersection if allowed to operate concurrently) depending upon vehicular demand by utilizing detectors placed in or near the intersection and the relevant portions of the traffic lanes entering into the intersection. Early traffic actuated controller units were of a sonic type. Located at the stop lines of an intersection, these detectors were responsive to a motorist blowing the vehicle&#39;s horn. Upon actuation, these controllers permitted the motorist to obtain the right-of-way. These early actuated controller units were essentially, however, modified pre-timed controller units which provided only a fixed length cycle upon actuation. 
     To improve intersection efficiency, control units were developed that could flexibly extend a cycle, within certain parameters, based upon vehicular demand. Detection units progressed from the early sonic type to pressure sensitive devices and electrical circuits that were embedded in the roadway and actuated by the weight of a passing vehicle or a change of inductance during passage of a vehicle. In addition to the above detection devices, current controller units utilize various detection methods, including sonar, radar, infrared, photo-electric cell, and magnetic devices for detecting vehicles in the portion of traffic lanes entering an intersection. 
     Although intersection efficiency has increased as a result of the technological progression in detection devices, current traffic signal systems continue to operate on a cycle by cycle basis for an intersection; each cycle consisting of one more progression phases for certain traffic lanes (i.e., proceed signals for permitting movement of certain traffic lanes through the intersection) and non-progression phases for the remaining traffic lanes (i.e., caution and halt signals for halting movement of the remaining traffic lanes through the intersection). FIG. 1 depicts typical traffic movements through intersection 100. 
     The introduction of microprocessors to controllers brought about major changes in traffic signal systems, including the ability to coordinate the movement of traffic through two or more signalized intersections. Coordination of two or more signalized intersections resulted in a number of benefits, including the ability to change timing plans to accommodate predominate traffic flows; to increase capacities of major arterials to meet peek demands; to control speeds on major arterials; and to conserve energy and improve safety by reducing stops and delays. Coordination among two or more intersections is typically accomplished by either a centralized controller system (i.e., a central controller performing all processing functions for each of the intersections) or a distributed controller system (i.e., two or more controllers responsible for controlling the signalized intersections assigned to such controllers and for further communicating between one another). Communications in a coordinated system are typically conducted through twisted pair cable, coaxial cable, fiberoptic cable, or radio transmission. The operation of current traffic controllers and the coordination of two or more signalized intersections is well known in the current art and the reader is directed to the publication entitled &#34;Participant Notebook&#34; dated Jul. 1993 for Traffic Control Equipment &amp; Software Demonstration Project, published by the United States Department of Transportation, Federal Highway Administration, for a more thorough discussion of current traffic controllers and the coordination of signalized intersections. 
     As can be seen in FIGS. 2a and 2b, the current art employs zones for detecting vehicles 225, 230, 235, 240, 245, 250, 255, and 260 entering intersection 200. Detection zones 245, 250, 255, and 260 typically include loop detectors (i.e., a detector that senses change in inductance of its inductive loop sensor caused by the passage or presence of a vehicle near the sensor), presence detectors (i.e., a detector which is able to detect the presence of a vehicle and maintain the detection signal for a predetermined period of time that the vehicle is within its field of detection), or a combination of loop and presence detectors. Detection zones 225, 230, 235, 240, 245, 250, 255, and 260 are limited to areas which are in close proximity to stop lines 205, 210, 215, and 220 for each traffic lane. This relatively close proximity of such detection zones to such stop lines requires vehicles approaching such an intersection in a traffic lane with a caution or halt signal showing to come to a near, or complete, stop before each vehicle&#39;s demand for a proceed signal is recognized and serviced by the controller for the intersection. Thus, the orderly progression of vehicles through such an intersection is often halted or delayed because a vehicle is required to wait for a proceed signal, although no demand for a proceed signal exists by vehicles in one or more conflicting traffic lanes. Also, current traffic signal systems do not monitor the portions of traffic lanes leaving the intersection to determine if the leaving portions are not blocked (i.e., free of vehicles) so that complete movement of vehicles through the intersection is possible. 
     A further limitation of the close proximity of the detection zones to the intersection is that current controllers and methods for operating a signalized intersection do not generally provide accident avoidance functions. That is, current controllers and methods for operating a signalized intersection do not monitor the portions of traffic lanes entering an intersection to determine the probability of a vehicle being able to pass through the intersection during a caution signal or to timely stop for a halt signal, nor do they attempt to clear the intersection, so as to prevent a possible accident if it is determined that a vehicle will not be able to pass through the intersection during a caution signal or to timely stop for a halt signal. 
     Therefore, a system and method is desired for controlling one or more signalized intersections in which delays to vehicular traffic are reduced by detecting the presence of a vehicle, determining if the vehicle can proceed completely through an intersection, and when possible, providing a proceed signal for the vehicle before the vehicle has come to a near, or complete, stop. A system and method is also desired which facilitates accident reduction by monitoring the probability of a vehicle being able to pass through an intersection or to timely stop for a caution or halt signal, respectively, and attempts to clear the intersection when it becomes likely that a vehicle will not be able to pass through the intersection or to timely stop for a caution or a halt signal, respectively. 
     SUMMARY OF THE INVENTION 
     The present invention includes a system and method for reducing delays to vehicular traffic through one or more signalized intersections and for facilitating accident reduction at such intersections. The present invention comprises detectors, such as a camera system, for detecting vehicles entering and leaving an intersection, a plurality of signals for controlling the movement of vehicles through the intersection, and at least one controller for controlling the plurality of traffic signals at one or more signalized intersections. The present invention may operate in either a centralized system or a distributed system. The present invention monitors the portions of traffic lanes entering and leaving each intersection for vehicles and generates signals that correspond to whether the detected vehicles are entering or leaving each intersection. The controller receives these signals and, preferably using the method of the present invention, controls the plurality of traffic signals to permit the efficient movement of traffic through each intersection and to facilitate accident reduction at each intersection. 
     The system monitors detection zones for portions of traffic lanes entering each intersection that comprise areas whose outer boundaries are at a distance from each stop line for each intersection. This permits detection of vehicles at a greater distance from each stop line than is conducted by the current art. Unlike the current art, the system also preferably monitors detection zones for portions of traffic lanes leaving each intersection to determine whether a vehicle is substantially proximate to the intersection, and thus, determine if there is sufficient room in the applicable traffic lane for another vehicle to proceed through and clear (i.e., not be present in) the intersection. 
     Further, the detection zones for portions of traffic lanes entering each intersection are sufficiently distant from each stop line to permit, when possible, the controller to process the detection signals and cause the display of a halt signal on the applicable traffic signals for all conflicting lanes of traffic entering the intersection and a proceed signal for the applicable lane of traffic entering the intersection upon the detection of a vehicle. Thus, the detected vehicle will not be required to come to a near, or complete, stop before receiving a proceed signal. The length of the detection zones for portions of traffic lanes entering the intersection also permit the controller to process the detection signals, and when vehicles are proceeding through the intersection, determine if a vehicle approaching the intersection in a traffic lane which conflicts with the traffic lane(s) for those vehicles proceeding through the intersection is capable of stopping before reaching the intersection. If a determination is made that the vehicle cannot stop before reaching the intersection, the system generates halt signals to all signals in an effort to facilitate accident reduction by clearing the intersection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings in which: 
     FIG. 1 depicts typical traffic movements at an ordinary intersection; 
     FIGS. 2a and 2b depict zones of detection employed by the current art for detecting vehicles in portions of traffic lanes entering an intersection; 
     FIG. 3 depicts the zones of detection employed by the present invention for detecting vehicles in portions of traffic lanes entering and leaving an intersection; 
     FIG. 4 depicts a system configuration for one embodiment of the present invention; and 
     FIG. 5 depicts a flow chart of the methodology for the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning to FIG. 3, a preferred embodiment of the invention for controlling movement of vehicles at an intersection includes detection zones 315, 316, 325, 326, 335, 336, 345, and 346 for detecting vehicles entering intersection 300 and detection zones 310, 320, 330, and 340 for detecting vehicles leaving intersection 300. It should be noted that detection zones 315, 316, 325, 326, 335, 336, 345, and 346 comprise areas whose outer boundaries are at a distance from stop lines 350, 355, 360, and 365, respectively, so as to permit detection of vehicles at a greater distance from stop lines 350, 355, 360, and 365, respectively, than is monitored by the current art (See 225, 230, 235, 240, 245, 250, 255, and 260 of FIGS. 2a and 2b). 
     The distance from stop lines 350, 355, 360, and 365 for detection zones 315, 316, 325, 326, 335, 336, 345, and 346 is sufficiently great to permit, when possible, the display of a halt signal for all conflicting lanes of traffic and a proceed signal for the applicable lane of traffic upon the detection of a vehicle within applicable detection zone 315, 316, 325, 326, 335, 336, 345, and 346 so that the detected vehicle will not be required to come to a near, or complete, stop before receiving a proceed signal. It should be noted that detection zones 316, 326, 336, and 346 will typically be of a shorter distance from stop lines 350, 355, 360, and 365 then detection zones 315, 325, 335, and 345 because such detection zones are for left turning traffic lanes. The preferred embodiment of the invention includes separate detectors for monitoring left turning traffic lanes. In other embodiments of the invention, the system does not include such separate detectors for monitoring left turning traffic lanes, but rather, includes a single detector. It should also be noted that detection zones 310, 320, 330, and 340 leaving intersection 300 are smaller than detection zones 315, 316, 325, 326, 335, 336, 345, and 346 and are sufficiently large to detect a vehicle that is substantially proximate to intersection 300 so that there is insufficient room in the applicable traffic lane for another vehicle to proceed through and clear (i.e., not be present in) intersection 300. 
     As shown in FIG. 4, a preferred embodiment of system 400 for controlling movement of vehicles through intersection 405 having a plurality of traffic lanes 410, 411, 412, and 413 (wherein each of the traffic lanes 410, 411, 412, and 413 includes a portion entering 415, 416, 417, and 418 intersection 405, a portion leaving 420, 421, 422, and 423 intersection 405, and a stop line 425, 426, 427, and 428 located in entering portions 415, 416, 417, and 418) includes a plurality of traffic signals 430, 431, 432, and 433 corresponding to each entering portion 415, 416, 417, and 418 of traffic lanes 410, 411, 412, and 413; a plurality of detection devices 435, 436, 437, 438, 439, 440, 441, and 442 for detecting the presence of vehicles in detection zones entering and leaving intersection 405 (See 310, 315, 316, 320, 325, 326, 330, 335, 336, 340, 345, and 346 of FIG. 3) wherein detection devices 435, 436, 437, 438, 439, 440, 441, and 442 are configured to generate a demand signal or a halt signal corresponding to the applicable traffic lane in which the vehicle is detected for entering portions 415, 416, 417, and 418 or leaving portions 420, 421, 422, and 423, respectively, of applicable traffic lane 410, 411, 412, and 413 in which the vehicle was detected; and controller 445 for receiving and processing the demand and halt signals from detection devices 435, 436, 437, 438, 439, 440, 441, and 442 and controlling traffic signals 430, 431, 432, and 433 to permit the movement of vehicles through intersection 405. 
     It should be noted that detection devices 435, 437, 439, and 441 may include separate detection devices for monitoring one or more individual traffic lanes of entering portions 415, 416, 417, and 418 and leaving portions 420, 421, 422, and 423. It should be further noted that traffic signals 430, 431, 432, and 433 may include separate signals for controlling the movement of traffic in one or more individual traffic lanes of entering portions 415, 416, 417, and 418. One embodiment of detection devices 435, 436, 437, 438, 439, 440, 441, and 442 preferably includes a camera system as disclosed in U.S. Pat. No. 5,438,360 titled Machine Vision Camera and Video Preprocessing System. Other embodiments of detection devices 435, 436, 437, 438, 439, 440, 441, and 442 may include sonar, radar, infrared, and/or magnetic detection means. One embodiment of controller 445 preferably includes the 3000 Series Advanced Nema Traffic Controller manufactured by Peek Traffic-Transyt of Tallahassee, Fla. 
     FIG. 5 depicts the overview of the methodology for controlling traffic signals 430, 431, 432, and 433 (See FIG. 4). The methodology begins 505 with setting all traffic signals to a halt indication 510. 
     If demand to enter the intersection is detected 515, a traffic lane flag is set which indicates the traffic lane in which the demand was detected 520. If demand for the traffic lane for which the traffic lane flag is set exists 525, a check for a conflicting demand to enter the intersection is conducted 540. 
     Steps 540, 541, 542, 543, 544, and 545 relate to handling conflicting demand to enter the intersection if such demand exists and comprise the following. First, a determination is made as to whether the detected vehicle with the conflicting demand is traveling at a rate of speed that will permit the vehicle to stop before arriving at the applicable stop line for the intersection 541. If not, all signals are set to halt in an effort to clear the intersection 510 and, thereby, facilitate accident reduction. If it is determined that the vehicle can stop before arriving at the applicable stop line, a determination is made as to whether a wait flag (i.e., an indication that conflicting traffic has been waiting to proceed through the intersection) has been set 542. If the wait flag has not been set, a counter for the period of time that conflicting traffic must wait before being allowed to proceed through the intersection is initialized and the wait flag is set 543. Step 543 is avoided if the wait flag was previously set. Next a determination is made as to whether the maximum amount of time that conflicting traffic must wait before being allowed to proceed through the intersection has transpired 544. If the wait time has not transpired, the demand signal generated by the conflicting traffic is ignored 544. If the wait time has transpired, then caution and halt signals, respectively, are displayed for traffic lanes associated with the traffic lane flag and the wait flag for conflicting traffic is cleared 545. 
     After determining if conflicting demand to enter the intersection exists 525 and servicing such demand if it does exist 541, 542, 543, 544, and 545, a determination is made as to whether non-conflicting demand to enter the intersection (i.e., demand from vehicles that would not interfere with the current demand if such vehicles were permitted to proceed through the intersection concurrently with the existing demand) exists 550. If such non-conflicting demand exists and if a predetermined amount of time remains before the wait time for conflicting demand (which was initialized in 543) transpires and if the portion of the applicable traffic lane leaving the intersection for the non-conflicting demand is not blocked (i.e., no vehicles are present in the applicable detection zone so as to prevent another vehicle from proceeding through and out of the intersection) 551, a proceed signal is displayed for those traffic lanes associated with the non-conflicting demand 552. 
     After determining if non-conflicting demand to enter the intersection exists 550 and handling such demand if it does exist 551 and 552, a determination is made as to whether the portion of the traffic lane associated with the traffic lane flag leaving the intersection is blocked 555. If the leaving portion of the traffic lane is blocked, the traffic lane flag is cleared 556 and a transfer to 526, which is discussed in detail below, is made. If the leaving portion of the traffic lane is not blocked, a proceed signal is displayed for the traffic lane 560 and a determination is once again made as to whether demand for the traffic lane for which the traffic lane flag is set exists 525. 
     If demand for the traffic lane for which the traffic lane flag is set does not exist 525, service associated with the traffic lane is terminated (i.e., caution and halt signals are displayed), and the traffic lane flag is cleared 526. A determination is then made as to whether non-conflicting demand to enter the intersection exists 527. If non-conflicting demand to enter the intersection does exist, it is allowed to enter the intersection 530 if sufficient time exists before conflicting demand must be serviced and if the progression lane(s) for such non-conflicting demand are not blocked 529. Service for non-conflicting demand to enter the intersection is terminated 531 when such demand no longer exists, if insufficient time exists before conflicting demand must be serviced, or if the progression lane(s) for such non-conflicting demand are blocked 529. A determination is then made as to whether conflicting traffic is waiting to enter the intersection 532, if so the wait flag is cleared, the traffic lane flag is set 533 and a transfer to determining whether non-conflicting demand exists is made 550. If there is no conflicting traffic waiting to enter the intersection, all signals are set to halt 510. 
     While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to one skilled in the art the various changes and modifications can be made therein without departing from the spirit and scope thereof.