Daytime running lamps

A daytime running lamp (DRL, also daytime running light) is an automotive lighting and bicycle lighting device on the front of a roadgoing motor vehicle or bicycle, automatically switched on when the vehicle is moving forward, emitting white, yellow, or amber light to increase the of the vehicle during daylight conditions.

Depending on prevailing regulations and vehicle equipment, the daytime running light function may be implemented by functionally specific lamps, by operating the low beam headlamps or fog lamps at full or reduced intensity, by operating the high-beam headlamps at reduced intensity, or by steady-burning operation of the front turn signals. Compared to any mode of headlamp operation to create the daytime running light, functionally dedicated DRLs maximize the potential benefits in safety performance and minimize fuel consumption, glare, motorcycle masking, and other potential drawbacks.

Numerous studies done worldwide since the 1970s have tended to conclude that daytime running lights improve safety. A 2008 study by the U.S. National Highway Traffic Safety Administration analysed the effect of DRLs on frontal and side-on crashes between two vehicles and on vehicle collisions with pedestrians, cyclists, and motorcyclists. The analysis determined that DRLs offer no statistically significant reduction in the frequency or severity of the collisions studied, except for a reduction in light trucks' and vans' involvement in two-vehicle crashes by a statistically significant 5.7%.

The daytime running light was first mandated, and safety benefits first perceived, in Scandinavian countries where it is persistently dark during the winter season. As ambient light levels increase, the potential safety benefit decreases while the DRL intensity required for a safety improvement increases. The safety benefit produced by DRLs in relatively dark Nordic countries is roughly triple the benefit observed in relatively bright America.

In many countries, every motorcycle's low beam headlamp has been wired to illuminate whenever the engine is running, either as a matter of law or of voluntary industry practice. Some motorcycling advocacy groups are concerned over the potential for reduced motorcycle conspicuity with the introduction of headlamp-based DRLs on cars and other dual-track vehicles, since it means motorcycles are no longer the only vehicles displaying headlamps during the day. Some researchers have suggested that amber DRLs be reserved for use exclusively on motorcycles, in countries where amber is not presently a permissible color for DRLs on any vehicles, while other research has concluded there is a safety disbenefit to two 90 mm x 520 cd DRLs on motorcycles in comparison to one 190 mm x 270 cd dipped (low) beam headlight. The latter result suggests that DRL luminous area may have an important influence on its effectiveness.

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