51¶¯Âþ

Truck drivers sometimes miss warning notices and smash into low railway
bridges, where they get stuck. Now Bill Corbett of Sheffield reckons he has an
answer (GB 2 334 802). Since conditioned reflexes make even tired drivers stop
at red traffic lights, he reasons that hanging a flexible rubber bar over the
road at bridge height, about 100 metres ahead of it, should work. When an
oversized vehicle strikes the bar, it turns on a red traffic light just in front
of the bridge, causing the driver to brake. The light will stay red a while,
giving the driver time to notice the low bridge warning.