Abstract
A method of evaluating direct seeing distances, when two vehicles meet on a straight road, has been applied to examples of the two common headlighting systems in current use: one representing British and American practice, and the other representing European practice.
It is shown that the British beam gives better seeing along the nearside road verge, the European beam gives better seeing along the centre of the road, and that straight ahead of the vehicle seeing is about the same with both types of beam. The sharper cut-off European beam is more affected by vertical misaim than the British beam and, when facing one another, seeing with the British beam is improved at the expense of seeing with the European beam.
A comparison of the double-lamp British system with a system in which the meeting beam comes only from the nearside lamp, tilted upward so that its forward horizontal intensity is the same as that from the two lamps, shows that throughout most of the meeting seeing distances are very nearly the same, even when the single lamp faces the double-lamp system. During the later stages of the straight-road meeting, however, recovery from the minimum seeing condition is more rapid when facing the single lamp.
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