Road Management & Engineering Journal
Road Management & Engineering Journal
December, 1999
TranSafety, Inc.
(360) 683-6276
Fax: (360) 335-6402

Questions & Answers: Daytime Running Lights

(This article is reproduced, with permission, from the website of the Insurance Institute for Highway Safety at

Daytime running lights (DRLs) are a crash avoidance feature new to vehicles sold in America, but they've been used for years in Canada and Scandinavia. DRLs help prevent crashes by making vehicles more conspicuous. U.S. law now permits but does not require DRLs, which turn on automatically when the ignition is started and are overridden when regular headlights are activated. DRLs typically are high-beam headlamps at reduced intensity or low-beam headlamps at full or reduced power. Tail lamps and/or turn signals also may be lit. In some vehicles, turn signals alone function as DRLs, especially when the headlamps are hidden.

  1. What are the safety advantages of DRLs?
  2. How effective are DRLs?
  3. Where are DRLs required?
  4. Are DRLs available on vehicles in the United States?
  5. Why has it taken so long to introduce DRLs in the United States?
  6. Will DRLs be effective in the United States?
  7. Will DRLs shorten headlamp bulb life or lower fuel economy?
  8. Will motorists be bothered by glare?
  9. Are motorcycles required to have DRLs?

1. What are the safety advantages of DRLs? Daytime running lights are a low-cost method to reduce crashes. They are especially effective in preventing daytime head-on and front-corner collisions by increasing vehicle conspicuity and making it easier to detect approaching vehicles from farther away.

2. How effective are DRLs? Nearly all published reports indicate DRLs reduce multiple-vehicle daytime crashes. Evidence about DRL effects on crashes comes from studies conducted in Scandinavia, Canada, and the United States. A study examining the effect of Norway's DRL law from 1980 to 1990, found a 10 percent decline in daytime multiple-vehicle crashes. 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. In a second study covering two years and 9 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. 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.

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. A small-scale fleet study conducted in the 1960s found an 18 percent lower daytime multiple-vehicle crash rate for DRL-equipped vehicles. Multiple-vehicle daytime crashes account for about half of all police-reported crashes in the United States.

3. Where are DRLs required? Laws in Canada, Denmark, Finland, Hungary, Iceland, Norway, and Sweden require vehicles to operate with lights on during the daytime. There are two types of laws. Canada's requires vehicles to be equipped with DRLs. The other type of law in effect in Denmark, Finland, Hungary, Iceland, Norway, and Sweden requires motorists to turn on their headlights if their vehicles do not have automatic DRLs. This kind of law applies to drivers only, and vehicles do not have to be specially equipped. In 1972, Finland mandated daytime running lights in winter on rural roads and a decade later made DRLs mandatory year-round. Sweden's law took effect in 1977, Norway's in 1986, Iceland's in 1988, and Denmark's in 1990. Hungary has required drivers on rural roads to operate with vehicle lights on since 1993. Canada requires DRLs for vehicles made after December 1, 1989. No U.S. state mandates DRLs, although some require drivers to operate vehicles with lights on in bad weather.

4. Are DRLs available on vehicles in the United States? Offered on a handful of 1995 domestic and foreign model passenger cars, pickups, and sport utility vehicles, daytime running lights are becoming a more common feature. They're standard on all 1999 GM, Lexus, Saab, Suzuki, Volkswagen, and Volvo models, as well as the Toyota Avalon, Camry Solara, Corolla, and Sienna. They are optional on the Toyota Camry and Tacoma and on some BMWs. GM offers retrofit DRL kits for vehicles that don't already have DRLs. The kits can be used on non-GM models, as well.

5. Why has it taken so long to introduce DRLs in the United States? Some state lighting laws inadvertently prohibited DRLs until the National Highway Traffic Safety Administration (NHTSA) agreed to permit automakers to offer them on vehicles sold in all 50 states. This action, which preempted the state laws, followed a petition filed by General Motors. The Institute had filed a similar petition based on studies showing that DRLs are an inexpensive way to reduce daytime collisions between vehicles. After initially granting this petition, NHTSA terminated rulemaking in 1988, saying that the matter wasn't clearly a national safety issue and that auto manufacturers "tended to oppose, rather than support, the proposal." NHTSA then changed course again, approving DRLs in 1993.

6. Will DRLs be effective in the United States? Countries where DRLs are required generally have lower levels of ambient light during winter and longer periods of dusk and dawn than the United States. Although studies have indicated that DRLs have reduced crashes in North America and Scandinavia, the impact they will have on U.S. crashes has not been fully determined since DRLs have been used only on a limited basis here. Positive effects found in Canada's evaluation of DRLs are important because most of Canada's population is at a lower latitude than Scandinavia. Also, American DRLs are brighter than European DRLs. This should increase visual contrast between vehicles and their backgrounds despite brighter daylight conditions.

7. 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 General Motors 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. NHTSA estimates that only a fraction of a mile per gallon will be lost, depending on the type of system used. General Motors estimates the cost to be about $3 per year for the average driver. Transport Canada estimates the extra annual fuel and bulb replacement costs to be $3-15 for systems using reduced-intensity headlights or other low-intensity lights and more than $40 a year for DRL systems using regular low-beam headlights.

8. Will motorists be bothered by glare? In most countries mandating DRLs, glare has not been an issue. However, some motorists in the United States have complained that the systems here are too bright. In response to these complaints, NHTSA has proposed reducing the maximum allowable light intensity from 7,000 to 1,500 candela, a value more in line with European DRLs.

9. Are motorcycles required to have DRLs? Federal law does not require motorcycles to have DRLs, although all manufacturers voluntarily equip their cycles with such lights. Some states including California require the lights, and 22 states require motorcyclists to ride with their headlights on at all hours.

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