Changing lights

Researchers Aaron Bachelder and Conrad Foster at Caltech have thought up two novel systems that could modify the switching of traffic lights to give priority to emergency vehicles.

Both systems would use inductive loops already installed in the roads to detect vehicles for timing the switching of the traffic lights.

The proposed systems could be used alone or to augment other automated emergency traffic-light systems that are already in use, including those that recognise flashing lights or siren sounds or that use information on the position of an emergency vehicle derived from the Global Positioning System (GPS).

The developers say that their new ideas overcome the inherent limitations of existing systems. Systems that detect flashing lights and siren sounds, they say, are limited in range, cannot ‘see’ or ‘hear’ well around corners, and are highly vulnerable to noise. GPS-based systems are effective in rural areas and small cities, but are often ineffective in large cities because of frequent occultation of GPS satellite signals by large structures.

In contrast, the engineers proposed traffic-loop forward prediction system would be relatively invulnerable to noise, would not be subject to significant range limitations, and would function well in large cities – even in such places as underneath bridges and in tunnels, where GPS-based systems do not work.

In their first idea, each participating emergency vehicle would be equipped with a computer and a radio transceiver that would communicate with stationary transceivers at the traffic loops.

Whenever an emergency vehicle was detected passing over a traffic loop, its transceiver would receive a position signal. The computer in the vehicle would then use the signal and the time of its receipt to estimate the position of the vehicle as function of speed and compass heading. At time intervals of 1 second, the transceiver would then broadcast the updated estimate of position to loop receivers at neighbouring intersections.

The stationary portion of the system would determine, on the basis of the updates, whether the vehicle was likely to pass through a given intersection within a suitable amount of time, in which case the system would switch the traffic lights at the intersection.

In the other system, a passive radio transponder would be installed on the underside of an emergency vehicle. When passing over a traffic loop, the transponder would be energised by a signal radiated via the loop. When energized, the transponder would transmit a vehicle identification.

Unlike the other system, there would be no continuous estimation of vehicle position. Instead, traffic lights would be changed on the basis of simple proximity detection. Once a vehicle had been detected at a loop at a given intersection, the detection would be signalled to neighbouring intersections. Traffic lights at the next intersection or next few intersections through which the vehicle could be expected to pass could then be changed until the vehicle passed through or until a specified time elapsed.

<b>This article was reproduced from NASA Tech Briefs by kind permission of the publishers.</b>.

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