U.S., EU Have Opposing Views on Daytime Running Lights
Reprinted from The Safety Record, Volume 6, Issue 3, June / July 2009
WASHINGTON, D.C. – The National Highway Traffic Safety Administration has rebuffed a nearly eight-year-old petition by General Motors to require daytime running lights on all passenger vehicles, saying that there is no credible statistical proof that the devices significantly improve safety.
“While DRLs may be beneficial for certain scenarios, the agency has been unable to document overall safety benefits due to DRL installation which could serve as a basis for mandating them,” the agency wrote in its denial.
GM had petitioned the agency in December 2001, based on two studies showing that daytime running lights significantly reduced multiple vehicle and vehicle-to-pedestrian crashes. The 2000 study showed a 5 percent decrease in the former category and a 9 percent decrease in the latter. The second study, which GM commissioned from Exponent in 2008, analyzed data regarding GM, Saab, Toyota, Subaru, Volkswagen and Volvo vehicles and 1996-2005 crash statistics from 18 states to examine the impact of DRLs on head-on, rural area, highway, rain/fog, angle, urban area, sideswipe, pedestrian, and motorcycle crashes. This study also found a significant reduction in crashes for vehicles equipped with DLRs: passenger cars saw a 12.35 percent decrease in head-on multiple vehicle crashes and a 9 percent decrease in rural daytime multivehicle crashes.
But NHTSA criticized the statistical methods used in both studies, saying one study used inappropriate parameters to create the sample. It dismissed some of the results of the other as pure bull – such as a claim in the Exponent study that DRLs would reduce night-time fatal crashes by 11.4 percent for passenger cars and daytime single-vehicle crashes by 9.4 percent for light trucks.
“These results cast doubt on the validity of the GM study because we do not believe these crash types are plausibly affected by DRL installation. The authors claim these numbers serve as useful control groups and benchmarks for comparison. The agency respectfully disagrees, and believes this may demonstrate the lack of control for changes that may have occurred during the study period.”
Depending on how the safety benefit was predicted, NHTSA’s own statistical studies, undertaken in 2000, 2004 and 2008, found varying degrees of safety benefits. In its rejection of the GM petition, the agency said that it was now basing its conclusions on analyses using a method called the ratio of odds ratio. (This was the statistical tool used in the much-criticized Exponent study.) In the 2004 NHTSA study, for example, when researchers used generalized statistical odds, “ a conventional statistical technique,” they found that daytime running lights reduced opposite direction daytime fatal crashes by 5 percent, reduced opposite direction/angle daytime non-fatal crashes by 5 percent; reduced non-motorists, pedestrians and cyclists, daytime fatalities in single-vehicle crashes by 12 percent; and reduced daytime opposite direction fatal crashes of a passenger vehicle with a motorcycle by 23 percent.
However, at the insistence of the study’s peer reviewers, the agency ran the numbers using the odds ratio technique. This produced a markedly different result, with the DRLs producing slight, but significantly insignificant, increases in crashes in vehicles so-equipped. The one positive, but notable exception, to this counter-intuitive result was the effect on crashes involving motorcycles. In this case, DRLs reduced daytime opposite direction fatal crashes of a passenger vehicle with a motorcycle by 26 percent.
The agency’s stance is surprising considering that the European Union is poised to make DRLs mandatory on all new vehicles by 2011. The EU’s rationale is also rooted in the results of studies, showing that these lights can reduce day-time crashes by up to 12 percent for passenger vehicles and 10 percent for motorcycles. Sweden was the first country to mandate daytime running lights in 1977, because of the country’s low light levels. The regulation then spread to the other Scandinavian countries. According to a 2004 EU report, 11 nations, including Canada and the sunnier locales of Israel and Italy require daytime running lights.
NHTSA’s study results are also in contradiction to a wealth of other studies, conducted in the U.S. and abroad, showing a measureable and significant safety benefit for daytime running lights. Some 14 studies, beginning in 1972, have found crash reductions ranging from 29 percent to 3 percent, depending on the type of crash. For example, a Norwegian study found a 10 percent reduction in multiple-vehicle daytime crashes. Two Danish studies, conducted after the nation began requiring them, found smaller, but similar decreases in day-time crashes and found left-turn crashes reduced by more than a third. Transport Canada also did research on this question, comparing 1990 model year vehicles equipped with daytime running lights to 1989 model year vehicles without them, and found a reduction of 11 percent.
The Insurance Institute for Highway Safety has been studying the effect of DRLs since 1985. The first study showed that commercial fleet passenger vehicles modified with DLRs experienced 7 percent fewer daytime multiple-vehicle crashes. A second IIHS study in 2002 of crashes in nine states found a 3 percent decrease in daytime crashes for DRL-equipped vehicles.
“I think the research is pretty clear,” says IIHS spokesman Russ Rader. “We didn’t submit a formal comment, but we did support making them mandatory. The benefit is small, but it is there.”
Nonetheless, this is the second time the agency has turned down a request to make DRLs mandatory. The IIHS petitioned NHTSA for their mandatory use in 1985. The agency granted the petition, then abruptly terminated the rulemaking in 1988, saying that the matter wasn’t “a national safety issue,” and that automakers opposed it. Then, in 1990, GM decided that it was for the installation of DLRs. Many state traffic laws prohibited the use of headlights during daylight hours, creating a formidable stumbling block. The automaker convinced NHTSA to override state laws and harmonize its regulations with Canada, which required them, with a new rule. Established in 1993, the amendment to FMVSS 108, permitting the voluntary application of daytime running lights, superseded those state laws.
The debate then turned to the limits on the intensity of the daytime beams. GM wanted a 7000 cd limit, in keeping with Canadian regulations. The agency resisted, fearing that the lights would visually obscure the turn signals and create unnecessary glare. In the Final Rule, the agency decided to reach a compromise, allowing a 7000 cd upper limit on upper beam , as long as they were mounted below the side mirror and inside the mirror mounting heights to avoid direct mirror glare from the rear. After GM installed the DLRs on all of their makes, including Saab and Saturn, the agency began to get complaints from motorists about the distracting glare. In 1998, the agency published an amendment, cutting the permitted intensity by more than half, to an upper limit of 3,000 cd.