Effects of headlight luminance and width between headlights on night driving distance estimation

The research reported here is part of a series of experiments that attempted to establish drivers' distance estimation accuracy during nighttime driving. The host car's lights are not only the host driver's main source of illumination, but also a source of distance information that other drivers use to estimate the distance between themselves and the host car's lights. To carry out this research, a photocell system was used to identify the cars' actual position. Sixty-four subjects were required to estimate a range of possible car locations from 60 to 80 m. The effects of headlight luminance and width between headlights were manipulated; more specifically, two levels of headlight luminance were used - namely High: 12 volts 4.4 amps. 258 lm., and Low: 8 volts 4 amps. 120 lm. There were also two levels of width - 1 and 2 m - between headlights. The results showed that subjects are really accurate at estimating the distance of moving and approaching vehicles when subjects are located in a stationary position. Width between headlights seems to play the most important role when estimating distance, while headlight luminance does not seem to play such a major role.