As a car drives along a road, its powered wheels load the surface in tension, stressing it severely. So Daedalus began to devise a fibre-reinforced road, its concrete loaded with graphite fibres, or modern alkali-resistant glass fibres. But these days, glass fibre is an optical medium. This reminded Daedalus of the serious information limits of many roads, particularly the narrow, winding roads of rural areas. A motorist stuck behind a slow vehicle on such a road can never overtake safely: he cannot see round the bends to check that the other side of the road is clear. Daedalus now intends to give him this information, using the glass reinforcing fibres in the road.

His plan is to lay the fibres not continuously, but in specific lengths — a kilometre say. At their ends, the fibres will be bent upwards to terminate on the road surface. Each fibre will then accept light from one end, and re-emit it a kilometre down the road. A vehicle on the road, by blocking the light entering the fibres, would produce a visible ‘road-shadow’ at this distance.

If the kilometre fibres were laid in overlapping sections, spaced (say) at 100-m intervals, then the road-shadow of a moving vehicle would step along the road a kilometre ahead in 100-m strides: a spatial brightness modulation. A stationary observer, or a car moving the other way, would see a flickering road-shadow. The faster the closing speed, the faster would be its perceived flicker. If shorter fibres — 500 m, 250 m, and so on — were also laid in the road, and at correspondingly closer intervals, then as the closing vehicle got nearer, the road-shadow modulation would speed up. With proper spacing of the fibres, a driver watching the other lane of the road could read a true ‘time of arrival’ of the closest vehicle on that lane. Flicker is easily seen even on a very bright object (hence the flicker photometer and the blink comparator). So no matter how the road wound and dipped, the driver would know if anything was coming, and how soon it would arrive. By watching his own lane, he would even learn about the vehicles behind and ahead of him.

This system has all the virtues. It is cheap, simple, lasts indefinitely, and has no electronics. It will work just as well in the dark, when the road-shadow will be replaced by a road-glow from the oncoming vehicle's lights. It is simple to interpret. It even strengthens the road.