Intersections traversed by vehicular traffic present a known heightened level of risk to people and vehicles entering the intersection. At intersections having significant levels of traffic, it is common to install a traffic signalling system to control flow of traffic through the intersection.
Traffic signalling systems installed on open roadways typically operate on one of a few common principles. A first type of traffic signal operates on a time sequence, such that e.g. red, yellow, and green signal lights are illuminated in some sequence, based on a timing system.
A second type of traffic signal generally displays the same set of lights, but maintains a default setting giving a green light indication to a primary road until such time as traffic in a corresponding secondary road enters a signal zone or otherwise triggers a changing of the lights. Triggering of changing of the lights may initiate a timing or other system for subsequently returning the lights to the default setting. A first triggering mechanism, taught in U.S. Pat. No. 4,908,615 Bayraktaroglu, relies on a radio signal transmitter mounted at the traffic signalling system to detect traffic entering the intersection, and a magnetic presence detector 98 embedded in the road to detect traffic present in the intersection.
A second triggering mechanism, taught in U.S. Pat. No. 2,130,013 Hunter, relies on detectors A and B embedded in the road.
The signal devices disclosed in the above references generally provide stop and go directives to one or more approach paths to the intersection. Such signal devices do not, in general, indicate whether any traffic is in or approaching the intersection.
U.S. Pat. Nos. 2,903,674 Schwab, and 5,187,476 Hamer teach devices whereby an emergency vehicle can take control of the signal lights as it approaches the intersection.
U.S. Pat. No. 3,881,169 Malach teaches a signal system including a device 15, 16 which discriminates with respect to vehicles meeting certain criteria, and accordingly takes control of the signal lights.
U.S. Pat. No. 4,115,757 Blahunka teaches a signalling system for use with lift trucks in an industrial environment, wherein a transmitter on the lift truck cooperates with a receiver on a signalling system over the intersection, thus activating a strobe light to indicate the presence of traffic approaching the intersection.
None of the known references teach or suggest any apparatus or methods for monitoring a signal zone about an intersection, detecting each target entering the signal zone, and giving warning display signals to traffic in approach paths outside the approach path occupied by the respective target.
It is an objective of this invention to provide a traffic signalling system, for monitoring a signal zone about an intersection having at least two approach paths, detecting each target entering the signal zone, and giving warning visual display signals to traffic in approach paths outside the approach path occupied by the respective target.
Another object is to provide a traffic signalling system adapted to direct a second visual display signal, different from the visual warning display, toward the approach path occupied by the respective target.
It is another object to provide a traffic signalling system adapted to indicate, in the visual warning displays, the approach path occupied by the respective target.
Still another object is to provide a traffic signalling system adapted to concurrently receive and process stimuli from first and second targets in respective first and second different approach paths, and to indicate to the targets in each of the respective approach paths, the presence of a second target in a second approach path.
Yet another object is to provide a traffic signalling system including timing apparatus for setting and running a delay timer which maintains the detection indication for the set time after the target has been detected.
A further object is to provide methods for signalling traffic using a traffic signalling system providing the features and advantages of the above disclosed objects.