Search Results

High-contrast brake lamps are lamps that appear black or body color when they are not energized. In addition to stylistic advantages, there may be some behavioral benefits from using high-contrast brake lamps, such as a reduction in driver reaction times to brake signals during high levels of ambient illumination. There are two possible mechanisms for such an effect. The first mechanism is based on the increased brightness difference between the off and on states. The second mechanism involves the increased color difference between the two states. While the standard brake lamp goes from darker red to brighter red, the high-contrast lamp appears to change from black or body color to red. The present study was designed to evaluate the potential reaction-time benefits of high-contrast brake lamps. The study, performed in a laboratory, simulated a daytime driving condition with illumination from the sun being reflected by the lenses of the brake lamps.

Body-color brake lamps are lamps that in their off state match the body color of the car. When energized, all body-color lamps, as well as conventional lamps, appear bright red. The speed of response to a body-color brake lamp may differ from the speed of response to a conventional lamp for two reasons. The first is that the difference between off-and on-state luminances varies primarily with off-state luminance. When the difference is larger than for the conventional lamp, the increased luminance contrast may speed reaction time. The other reason that responses for the two types of lamps may differ is the greater chromaticity contrast that body-color lamps have between their on and off states. This study separately evaluated the effects of luminance contrast and chromaticity contrast for body-color brake lamps.

In two experiments, we examined the possibility that rearview mirror reflectivity influences drivers' perceptions of the distance to following vehicles. In the first experiment, subjects made magnitude estimates of the distance to a vehicle seen in a variable-reflectance rearview mirror. Reflectivity had a significant effect on the central tendency of subjects' judgments: distance estimates were greater when reflectivity was lower. There was no effect of reflectivity on the variability of judgments. In the second experiment, subjects were required to decide, under time pressure, whether a vehicle viewed in a variable-reflectance rearview mirror had been displaced toward them or away from them when they were shown two views of the vehicle in quick succession. We measured the speed and accuracy of their responses. Mirror reflectivity did not affect speed or accuracy, but it did cause a bias in the type of errors that subjects made.

Conventional brake lights require 250 msec to reach 90% intensity, thereby causing potentially important delays of warning information to following drivers. Several improvements are possible, including the use of LED displays. LED's, however, are more expensive than conventional incandescent bulbs and require redesign of lamp housings. As an alternative, we have designed a simple and relatively inexpensive circuit that produces a faster warning signal using a conventional bulb. We have evaluated the benefits of this device in a laboratory study that measured subjects' reaction times to the onset of brake lights in a simulated car-following situation. Our data indicate that the benefit of the device is on the order of 115 msec. For a vehicle traveling at 65 miles per hour, that benefit translates to a decrease in stopping distance of 11 feet.

In a static field study we tested drivers’ abilities to detect vehicles in the periphery of their direct fields of view while they gazed toward the driver-side exterior rearview mirror of a passenger car. The results indicate that both younger and older drivers can detect vehicles with reasonable efficiency even in far peripheral vision. However, the results also indicate that using peripheral vision entails a cost in terms of lengthened reaction time. Although that cost seems modest in comparison with the normal durations of glances to rearview mirrors and of direct looks to the rear, it is not clear from this study alone how the reaction time cost might influence the scanning strategies that drivers actually use in driving. The present study was oriented more to testing drivers’ basic visual capabilities than to outlining their overall strategies.