Q&A: Daytime running lights

March 2013

1 What are daytime running lights, and what safety benefits do they provide?

Daytime running lights (DRLs) are headlights that are lit whenever a vehicle is running. A low-cost method to reduce crashes, they are especially effective in preventing daytime head-on and front-corner collisions by making it easier to see vehicles, particularly as they approach from far away.

2 Where are DRLs required?

Laws in Canada and many European countries require vehicles to operate with lights on during the daytime. Canada requires vehicles made after Dec. 1, 1989, to be equipped with DRLs. The European Union requires DRLs for new cars and small vans under a law that took effect in February 2011. New trucks and buses in the EU must have DRLs starting in August 2012.

No U.S. state mandates DRLs, but some require drivers to operate vehicles with lights on in bad weather.

3 Are DRLs available on vehicles in the United States?

First offered on a handful of 1995 domestic and foreign model passenger cars, pickups and SUVs, daytime running lights have become a more common feature. They are standard on all General Motors, Lexus, Mercedes-Benz, Saab, Subaru, Suzuki, Volkswagen and Volvo models. Other manufacturers also offer daytime running lights on certain models. GM offers retrofit kits for vehicles that do not already have DRLs. The kits can be used on non-GM models, too.

4 How effective are DRLs?

Nearly all published reports indicate DRLs reduce multiple-vehicle daytime crashes. A study examining the effect of Norway's DRL law from 1980 to 1990 found a 10 percent decline in daytime multiple-vehicle crashes. Elvik, R. 1993. The effects on accidents of compulsory use of daytime running lights for cars in Norway. Accident Analysis and Prevention 25(4):383-98. A Danish study reported a 7 percent reduction in DRL-relevant crashes in the first 15 months after DRL use was required and a 37 percent decline in left-turn crashes. Hansen, L.K. 1993. Daytime running lights in Denmark: evaluation of the safety effect. Copenhagen, Denmark: Danish Council of Road Safety Research. In a second study covering two years and nine months of Denmark's law, there was a 6 percent reduction in daytime multiple-vehicle crashes and a 34 percent reduction in left-turn crashes. Hansen, L.K. 1994. Daytime running lights: experience with compulsory use in Denmark. Proceedings of the Fersi Conference. Copenhagen, Denmark: Danish Council for Road Safety Research. A 1994 Transport Canada study comparing 1990 model year vehicles with DRLs to 1989 vehicles without them found that DRLs reduced relevant daytime multiple-vehicle crashes by 11 percent. Arora, H.; Collard, D.; Robbins, G.; Welbourne, E.R.; and White, J.G. 1994. Effectiveness of daytime running lights in Canada. Report no. TP-12298. Ottawa, Ontario: Transport Canada.

In the United States, a 1985 Institute study determined that commercial fleet passenger vehicles modified to operate with DRLs were involved in 7 percent fewer daytime multiple-vehicle crashes than similar vehicles without DRLs. Stein, H. 1985. Fleet experience with daytime running lights in the United States. SAE Technical Paper Series 851239. Warrendale, PA: Society of Automotive Engineers. A small-scale fleet study conducted in the 1960s found an 18 percent lower daytime multiple-vehicle crash rate for DRL-equipped vehicles. Cantilli, E.J. 1970. Accident experience with parking lights as running lights. Highway Research Record 332:1-13. Washington, DC: Transportation Research Board. Multiple-vehicle daytime crashes account for about half of all police-reported crashes in the United States. A 2002 Institute study reported a 3 percent decline in daytime multiple-vehicle crash risk in nine U.S. states concurrent with the introduction of DRLs. Farmer, C.M. and Williams, A.F. 2002. Effects of daytime running lights on multiple-vehicle daylight crashes in the United States. Accident Analysis and Prevention 34(2):197-203.

Federal researchers, using data collected nationwide from 1995 to 2001, concluded that there was a 5 percent decline in daytime, two-vehicle, opposite-direction crashes and a 12 percent decline in fatal crashes with pedestrians and bicyclists. Tessmer, J.M. 2004. An assessment of the crash-reducing effectiveness of passenger vehicle daytime running lamps (DRLs). Report no. DOT HS-809-760. Washington, DC: National Highway Traffic Safety Administration. However, a 2008 federal study concluded that DRLs have no significant effect on either of these crash types. Wang, J.S. 2008. The effectiveness of daytime running lights for passenger vehicles. Report no. DOT HS-811-029. Washington, DC: National Highway Traffic Safety Administration.

5 Will DRLs shorten headlamp bulb life or lower fuel economy?

Running vehicle lights in the daytime does not significantly shorten bulb life. Systems like those on GM cars that use high beams are designed to operate at half their normal power during daylight hours, thereby conserving energy and reducing the effect on a vehicle's fuel economy. The National Highway Traffic Safety Administration (NHTSA) estimates that only a fraction of a mile per gallon will be lost, depending on the type of system used. 

6 Are motorcycles required to have DRLs?

Federal law does not require motorcycles to have DRLs, but some states require motorcyclists to ride with their headlights on at all hours. Since 1979 most manufacturers have equipped their cycles with automatic-on headlamps.