Citation

Roper VJ. Highw. Res. Board bull. 1953; 68: 16-30.

Copyright

(Copyright © 1953, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

The glass used in heat-absorbing windshields currently available transmits 18 percent less light than ordinary windshields. This reduction in light transmission led to concern about the possibility of a serious reduction in nighttime-seeing distances, which are barely sufficient, at best. Tests were conducted on an airstrip, using two identical cars equipped with sealed-beam headlamps. Ordinary and heat-absorbing windshields were interchanged in the two cars. Observations were made while driving at 40 mph., half with each type of windshield. Seeing-distance observations were made both against the glare of an approaching car and when the road was clear. A summary of these observations shows an average reduction in seeing distance of not quite 6 percent for driving with no approaching vehicle and an average reduction of 2 percent when approaching another car on a straight, level road over a distance of almost a mile. For the most critical portion of the seeing-distance curve, the last 500 ft. Before meeting an approaching car, results show the same seeing distances through ordinary and heat- absorbing windshields. This may be explained by the slight reduction in brightness of the approaching headlamps as offsetting the reduction in brightness of the obstacles under observation. Both reductions are caused by the 18- percent additional absorption of light by the heat-absorbing glass. As a result of these data, it may be argued that unless the driver does practically all of his driving at night, the daytime benefits to be derived from the heat- absorbing glass windshield offset the small reduction in seeing distance at night. This reduction averaged 3 percent over the entire seeing-distance curve obtained in the tests reported as a result of the investigation. Absorption; Brightness; Drivers; Headlamps; Heat; Light; Night visibility; Sight distance; Testing; Transmissions; Vision; Windshields