Variable speed limit system

Details Variable speed limit system Variable speed limit system

2002-10-21

2004-11-30

Hofsass, Jeffery (Department: 2636)

Communications: electrical

Vehicle detectors

Speed and overspeed

C340S933000

Reexamination Certificate

active

06825778

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a traffic control system and more particularly to a system that can automatically determine appropriate speed limits at various locations.
BACKGROUND OF THE INVENTION
It is well known that many people are injured annually as a result of motor vehicle crashes in construction work zones, and many of those injuries result in fatalities. Drivers not paying attention and excessive speed are the leading factors in these accidents, over 40% of which happened in the transition area before the construction work zone. The transition from high speed, open road traffic to reduced speeds at points of traffic congestion and construction sites, etc., can result in rapid deceleration or rear end accidents, and uneven traffic flow, while reducing capacity and possibly enabling unsafe speeds in construction work zones.
The prior art has attempted to solve this problem by the use of portable light signalling equipment. Such portable light signalling equipment has been used for both regulating traffic at restricted points and as a replacement for defective stationary equipment. Frequently, it is observed that movable traffic lights of this kind, which are required at building sites, for example, are not optimally adapted to the traffic flow, and as a result cause unnecessary delays to much of the traffic, particularly when the traffic flow is fluctuating. Generally, conventional portable light signalling equipment includes equipment that does not have any optional feedback system. The “stop”, “go” and clearance times are pre-programmed and are usually only very broadly adapted to the actual traffic, and are invariant in their daily operation. Centrally controlled and monitored equipment, with passive light signalling equipment, allows the signal to be set by feedback. However, such equipment requires expensive cabling, the size of which has to be adapted to the power (including the current supply to the lights) to be transmitted. For example, U.S. Pat. No. 6,124,807, issued Sep. 26, 2000, to R. Heckcroth et al, provides a procedure for regulating traffic by means of movable light signalling equipment. The movable signals are placed at restricted areas, and use sensor controls to prescribed “go” times and clearance times in the area to be secured (i.e., along a blocked stretch). The transit time of vehicles, over a measured distance extending substantially along the blocked stretch, is measured and the clearance time is established as a function of the transit time measurements obtained.
It is also known to use an apparatus for controlling two traffic lights at either end of a work zone. Axle counters are provided that switch the apparatus over by means of counters whenever there is a coincidence between two counting circuits (i.e., when the number of the counted vehicles leaving the restricted area equals the number of the vehicles that entered the area). However, there can be malfunctions if vehicles remain in the restricted area, or enter the restricted area outside of the surveillance points. In such cases, the equipment has to be restarted. Moreover, such equipment does not provide separate “go” and clearance times. For example, U.S. Pat. No. 5,900,826, issued May 4, 1996 to Farber, discloses a signalling system for controlling two-way traffic flow around a construction zone. The system consists of two traffic lights at opposite ends of a construction zone that are alternately activated to give a green light to oncoming traffic. The lights communicate through a wireless link. The lights are also provided with sensors that detect whether a vehicle is attempting to go through on a red light. When such a vehicle is detected, an audible warning signal is activated.
In another prior art system, traffic signals and detectors, e.g., pressure sensors at both ends of a restricted section, are provided for detection of the number of vehicles passing through. The signalling time of green signals is extended at the heavier traffic end. A signal controller circuit includes a signal device that changes the signal indication by means of vehicle detector, e.g., light sensors or the like, provided adjacent to the signals. Further, a system is known for an alternately switched traffic signal controller having a set of traffic signals which are operated such that while one traffic light at the “passage allowed” end is green, the other traffic signal at the “no passage allowed” end is red, or against. Detectors are provided for detection of vehicles passing through the section. Furthermore, a traffic signal device is also provided at both ends of a road section under construction. In such systems, the waiting time is still comparatively long, thus easily causing traffic jams when traffic density is distinctly larger at one side than at the other side in the road repairing section.
In addition, sensitive systems have been employed for control of the lighting of the traffic signals based on the detection of vehicles by the detector, e.g., pressure sensors, light sensors or the like. The control systems for traffic signals can be damaged in case of troubles in the detector means. Furthermore, as such signal systems are usually still in operation even at night when no vehicles are present, there is sometimes no input of detection signals for more than a pre-set time. In such a case, it cannot be concluded merely from the fact of no traffic that the detector means are out of order. Additionally, vehicles from the opposite directions can be exposed to great danger of head-on collision in the case that a vehicle enters the section against a red signal immediately after the change to red from green, while another vehicle also enters the section because of the signal change to green from red before the passing of the opposite vehicle.
Portable traffic control systems that are particularly suited to controlling traffic in work areas have also been disclosed. Normally, the systems are used on roads that have two traffic lanes, each for traffic in a different direction. When repair work is being performed on one lane of the road, however, the traffic in both directions must use the other lane. The control systems employ traffic lights at each end of the traffic lane, alternately presenting a “go” signal first to traffic from one direction and then to traffic from the other direction. The signals are viewable not only by oncoming traffic but also by an operator standing between the display units.
Another known device is intended to alert work zone personnel when a vehicle enters the work zone. This device is configured to detect the intrusion of a vehicle into the work zone along any section of the work zone perimeter adjacent to an active traffic lane. An infrared source is placed at the beginning of the work zone, which transmits a continuous wave infrared signal along the perimeter of the work zone for reception by an infrared detector positioned downstream. If a vehicle passes between the source and the detector, thereby interrupting the continuous wave infrared signal which is transmitted therebetween, the detector acknowledges this obstruction by sounding an alarm. However, this device also suffered numerous problems in operation.
This device suffers from several integrity problems. The heat and audible noise produced by work zone equipment, passing traffic, and other conditions of the work zone environment is capable of interfering with the infrared or ultrasonic detectors in such a way that the detectors can fail to detect a vehicle passing through the detection beam. Because the detector is designed to sense the presence or absence of a reflected detection beam, the detector is susceptible to detecting the heat or noise produced in the work zone as the reflected detection beam, even when the detection beam is obstructed by a vehicle entering the work zone. This is particularly true where the detector employs a continuous infrared signal. Thus, the potential always exists for a vehicle to pass through the detection beam without sounding the alarm, and without a

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