Communications: electrical – Traffic control indicator
Patent
1990-11-08
1992-04-28
Ng, Jin F.
Communications: electrical
Traffic control indicator
340932, 340928, G08G 108
Patent
active
051092247
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a road traffic signalling system, and in particular to a system for signalling individually to vehicles in a flow of traffic.
2. Description of Related Art
A major factor influencing road safety is the difficulty drivers of vehicles face in assessing distance, in particular a safe distance to the vehicle ahead. In conditions of poor visibility, such as fog, the problem is exacerbated by the lack of visual reference points from which a driver can judge his speed and it is well established that multiple crashes are often caused when successive vehicles in a flow of traffic become too closely spaced in relation to their speed.
International (PCT) Patent Publication No. WO-88/07560 describes a vehicle guidance and proximity warning system in which a series of "cat's eye" units embedded in the road are interconnected by optical fibres. The light received by any one unit from the headlights of an approaching vehicle is transmitted to neighbouring units. By transmitting light in a forward direction (relative to the direction of travel) the path of the road ahead is lit up. Alternatively, by transmitting light in a rearward direction, a warning is provided to a following vehicle of the vehicle ahead. Although the rearward lights provide an improved indication of traffic ahead in conditions of poor visibility, a simple passive system of this type can make no assessment of vehicle speed--an essential factor in determining the safe distance between vehicles.
A more complicated system, described in United Kingdom Patent Specification No. 1,090,091, provides for the illumination of lights in "cat's eye" units both ahead of and behind a vehicle. Two forward lights are arranged to come on after respective fixed delays from the detection of a vehicle, so that if the vehicle is exceeding a speed limit determined by the time delay and the separation of the light units, the vehicle will literally "over-ride" the lights and they will not be visible to the driver. Thus, although vehicle speed is not itself measured, an indication of speed in excess of a preset limit is provided. Each vehicle detected also causes to be set up a fixed pattern of "tail" lights to the rear of the vehicle. These tail lights are colour-coded according to the distance from the vehicle, so that a following driver receives an indication of his distance from the vehicle ahead as he closes up on it. However, the distance signals are fixed and take no account of vehicle speed. Thus, in order to judge a safe distance from the vehicle ahead, and assuming he does not over-ride his own forward lights, a driver has to take account of his own speed and the distance to the vehicle ahead, based on which of the tail signals associated with that vehicle are visible to him. There is no direct indication of safe distance as determined from measurement of vehicle speed.
SUMMARY OF THE INVENTION
It is an object of this invention, therefore, to provide an improved road traffic signalling system to warn vehicle drivers of unsafe traffic conditions, in particular in relation to vehicle position and speed.
According to the invention there is provided a road traffic signalling system for signalling individually to vehicles in a flow of traffic, the system comprising a succession of electronic signalling units positioned at intervals along a road, each unit comprising: vehicle detected at a unit ahead, timing means and to a said coded signal received by the communicating means, to control the signalling means in response to traffic conditions.
For respective pairs of adjacent units, the timing means of the forward unit is preferably controlled in response to the successive detections of a vehicle at the rearward unit and the forward unit to give a time interval indicative of vehicle speed past the forward unit. Alternatively, the timing means may be adapted to determine vehicle speed by measuring a time interval during which the output of the detector exceeds a predetermined threshold value.
REFERENCES:
patent: 3052869 (1962-09-01), Mountjoy
patent: 3078944 (1963-02-01), Gray
patent: 3302168 (1967-01-01), Gray et al.
patent: 3921127 (1975-11-01), Narbaits-Jaureguy et al.
patent: 3944912 (1976-03-01), Angel et al.
GEC--Marconi Limited
Ng Jin F.
Tumm Brian R.
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