TRIALS have shown that road vehicles which have stopped on level crossings can be detected by ultrasonics. Stationary or stalled vehicles cause a quarter of the 350 level crossing accidents which occur each year in Japan, and automatic detection linked to signals could avoid or mitigate many of these incidents.

Since an array of ultrasonic detectors was installed by JR Central in 1994 at Furukawa, they have worked effectively despite this being an area of heavy snowfall. Detectors based on light beams or induction coils under the road surface can be triggered by deep snow.

Ultrasonic transmitter/detector heads mounted 5 to 6m above the road surface project a 26kH signal vertically downwards at 95dB sound pressure level. The time taken for the echo to return indicates the height of the object below, and if it is more than 0·5m above the road surface, a vehicle is assumed to be on the crossing. If it remains there for more than a set time, indicating that it has stopped, approaching trains get a warning signal. The area of road scanned is a circle 1·2m in diameter.

There have been no false detections at the Furukawa crossing, which is on a non-electrified line. Last year, more powerful 124dB detectors were installed 8·5m above the road surface at crossings operated by JR Kyushu and JR Hokkaido. These will demonstrate the effectiveness of ultrasonic vehicle detection on electrified lines where they have to be mounted above the catenary.

Matsushita Communication Industrial Co Ltd

Reader Enquiry Number 137