Daytime Running Lights: The Studies

This page lists any studies for and against the government mandating Daytime Running Lights (DRL) and DRL in general. Anything in [ ] and italics are rebuttals from the other side. Please fell free to send me additions or rebuttals for this page by using this form or by emailing me. I can be reached to

Also be sure to check out Daytime Running Lights: The Arguments.


Summary of Research: DRLs are Proven Effective

DRLs, at sufficient levels of intensity, increase visual contrast between vehicles and their background. Various studies have shown that DRLs can improve the noticeability and detectability of vehicles in the central and peripheral fields of view. U.S. Department of Health and Human Services, Public Health Reports , Vol. 110 ; No. 3 ; Pg. 233; ISSN: 0033-3549 (May, 1995); Allen, J. M., Strickland, J., Ward, B., and Siegel, A.: Daytime headlights and position on the highway. Am J Optometry 46: 33--36 (1969); Attwood, D. A.: Daytime running lights project, IV: Two-lane passing performance as a function of headlight intensity and ambient illumination. Technical Report RSU 76/1. Defense and Civil Institute of Environmental Medicine, Downsview, Ontario, Canada, 1976; Attwood, D. A.: Daytime running lights project, II: Vehicle detection as a function of headlight use and ambient illumination. Technical Report RSU 75/2. Defense and Civil Institute of Environmental Medicine, Downsview, Ontario, Canada, 1975; Horberg, U.: Running light--twilight conspicuity and distance judgement. Report 215. Department of Psychology, University of Uppsala, Sweden, 1977; Horberg, U., and Rumar, K.: Running lights--conspicuity and glare. Report 178. Department of Psychology, University of Uppsala, Sweden, 1975; Kirkpatrick, M., Baker, C. C., and Heasly, C. C.: A study of daytime running lights design factors. (DOT HS 807 193). National Highway Traffic Safety Administration, Washington, DC, 1987.; Ziedman, K., Burger, W., and Smith R.: Evaluation of the conspicuity of daytime running lights. (DOT HS 807 609). National Highway Traffic Safety Administration, Washington, DC, 1990.

International Studies

Andersson, K., Nilsson, G., and Salusjarvi, M.: The effect of recommended and compulsory use of vehicle lights on road accidents in Finland. Report 102A. National Road and Traffic Research Institute, Linkoping, Sweden, 1976.
A study in Finland conducted between 1968 and 1974 found that DRLs, when required on rural roads in the winter, were associated with a 21-percent reduction in daytime multiparty crash events (involving more than one motor vehicle or motor vehicles colliding with pedestrians or pedalcyclists).

Andersson, K., and Nilsson, G.: The effect on accidents of compulsory use of running lights during daylight hours in Sweden. Report 208A. National Road and Traffic Research Institute, Linkoping, Sweden, 1981.
In Sweden, a study based on 2 years of pre-law and 2 years of post-law data reported and 11-percent reduction in multiparty daytime crashes subsequent to the DRL law.

Vaaje, T.: Kjorelys om dagen reducerer ulykkestallene. Arbetsdokument 15.8.1986. Transportokonomisk institutt, Postboks 6110 Etterstad, N-0602 Oslo 6, Norway, 1986.
A study in Norway published in Norwegian and reviewed by Koornstra found a 14-percent drop in multiparty crashes prior to the law, during the 1980-85 period when voluntary DRL use was climbing.

Elvik, R.: The effects on accidents of compulsory use of daytime running lights for cars in Norway. Accid Anal Prev 25: 383-398 (1993).
A study in Norway, covering the period 1980 to 1990, examined the effect of the country's DRL law, which applied to new cars in 1985 and to all cars beginning in 1988. DRL use was estimated to be about 30-35 percent in 1980-81, 60-65 percent in 1984-85, and 90-95 percent in 1989-90, so, as in the earlier Scandinavian studies, only partial implementation of DRLs was assessed. There was a statistically significant 10-percent decline in daytime multiple-vehicle crashes associated with DRLs in this study, excluding rear-end collisions, which increased by 20 percent. For all daytime crashes involving multiple parties, there was a statistically significant 15-percent reduction associated with DRLs in the summer but not in the winter. No significant effects of DRLs were found for collisions involving pedestrians or motorcyclists.

Hansen, L. K.: Daytime running lights in Denmark--Evaluation of the safety effect. Danish Council of Road Safety Research, Copenhagen, 1993; Hansen, L. K.: Daytime running lights: Experience with compulsory use in Denmark. Fersi Conference, Lille, 1994.
Two studies evaluating Denmark's 1990 DRL law have been completed, one that assessed short-term effects, the other looking at longer term effects. Results of these two studies were quite consistent. There was a small reduction in daytime multiple-vehicle crashes (7 percent) in the first year and 3 months the law was in effect, with one type of DRL-relevant crash (left turn in front of oncoming vehicle) reduced by 37 percent. In the second study, which covered 2 years and 9 months of the law, there was a 6-percent reduction in daytime multiple-vehicle crashes, and a 34-percent reduction in left-turn crashes. There was a small reduction in motor vehicle-pedalcyclist collisions (4 percent) but a statistically significant increase (16 percent) in motor vehicle-pedestrian collisions.

North American Studies

Some DRL critics have attempted to undermine the unequivical results of international studies on the grounds that driving conditions in Scandinavian countries are not comparable to North American driving conditions. The following studies utterly refute this assertion

Cantilli, E. J.: Accident experience with parking lights as running lights. Highway Research Record Report No. 32. National Research Council, Transportation Research Board, Washington, DC, 1970.
In the United States, a small-scale fleet study conducted in the 1960s found an 18-percent lower daytime, multiple-vehicle crash rate for DRL-equipped vehicles.

Stein, H. S.: Fleet experience with daytime running lights in the United States. Technical Paper 851239. Society of Automotive Engineers, Warrendale, PA. 1985.
In a much larger fleet study conducted in the 1980s, more than 2,000 passenger vehicles in three fleets were equipped with DRLs.

One fleet operated in Connecticut, another in several States in the Southwest, and the third operated throughout the United States. A 7-percent reduction was found in daytime multiple-vehicle crashes in the DRL-equipped vehicles compared with control vehicles.

Aurora, H., et al.: Effectiveness of daytime running lights in Canada. TP 12298 (E). Transport Canada, Ottawa, 1994.
In a study in Canada comparing 1990 model year vehicles (required to have DRLs) with 1989 vehicles, a statistically significant 11-percent reduction in daytime multiple-vehicle crashes other than rear-end impacts was estimated. This estimate was adjusted to take into account the fact that about 29 percent of 1989 vehicles were fitted with DRLs. Collisions involving pedestrians, pedalcyclists, motorcyclists, and heavy trucks and buses were not included in this study.

Sparks, G. A., et al.: The effects of daytime running lights on crashes between two vehicles in Saskatchewan: a study of a government fleet. Accid Anal. Prev 25: 619-625 (1991).
In another Canadian study, crashes of vehicles with and without DRLs in a government fleet in Saskatchewan were compared with a random sample of crashes involving vehciles without DRLs. The estimated reduction in daytime two-vehicle crashes was 15 percent. When the analysis was limited to two-vehicle collisions most likely to be affected by DRLs--involving vehicles approaching from the front or side--the estimated reduction was 28 percent.

Society of Automotive Engineers Inc., Automotive Engineering Vol. 102 ; No. 8 ; Pg. 35; ISSN: 0098-2571 (August, 1994).
In 1994 Avis, Inc. announced the results of a traveler-safety study analyzing the incidence and degree of damage to cars equipped with daytime running lights; the study showed a significantly greater degree of damage to those without daytime running lights (DRLs). Those equipped with DRLs have their headlights on at all times and are more visible to other drivers. During the day, they are on at an 80% power level; in the dark they operate at 100%.

Damage severity in the non-DRL group (measured in terms of cost) was 69% greater than that of the DRL-equipped fleet. Only the non-DRL vehicles experienced damage in excess of $15,000. The Avis study involved 1500 cars with DRLs, and 1500 without, representing approximately 29,000 rentals in eight cities in Maine, Michigan, Minnesota, New York, Oregon, and Washington.

Summary of the Studies

U.S. Department of Health and Human Services, Public Health Reports , Vol. 110 ; No. 3 ; Pg. 233; ISSN: 0033-3549 (May, 1995).
In summary, although the studies of DRLs have differed in design, analysis techniques, and outcome measures, the later studies are largely in accordance with the earlier ones, indicating that the overall effect of DRLs on motor vehicle crashes is positive.

Duration of DRL Effects

An often-used anti-DRL argument is that the positive effects of DRLs will erode over time as the public becomes accustomed to their use on the roadways. The following analysis proves this argument to be fallacious.

U.S. Department of Health and Human Services, Public Health Reports , Vol. 110 ; No. 3 ; Pg. 233; ISSN: 0033-3549 (May, 1995).
The early and later DRL studies have shed light on concerns about the duration of DRL effects and the possibility of negative effects of DRLs on some road users. It has been suggested that when DRLs are first introduced into some part of the vehicle population, positive crash reduction effects will be found only because DRLs are new and unique and the vehicles that have them stand out from those that do not. Once people get used to seeing vehicles with DRLs, it is conjectured, their effects will diminish, and, if all vehicles have them, their noticeability will be reduced or drivers will come to ignore the extra information.

All three of the early Scandinavian studies examined the effects of DRLs over a period of several years when DRL use was increasing, and DRL effects were estimated in Sweden and Finland when DRL use was nearly 100 percent. Thus to the extent that novelty or habitation effects occur, the effects of DRLs in the early Scandinavian studies were still positive over time and with close to 100 percent use. The later studies also suggest that the initial positive effects of DRLs do not dissipate over time. The reductions in multiple-vehicle crashes found in the Denmark studies, based on experience during the first 15 months of the law and then extended to include the first 33 months, were very similar. This similarity led the author to onclude that the effect was a permanent one and not due to the novelty of DRLs. In the study in Norway, the reduction in daytime multiple-vehicle crashes was maintained during the 3 years in which DRLs were required for all vehicles and use was close to 100 percent.

Effect of DRLs on Motorcyles

Another anti-DRL argument is that their use in automobiles will negate the positive effects of motorcycles operating with their lights on. The following studies indicate that this argument has little statistical weight.

The effect of DRLs on motorcycle crashes has been studied in Denmark and Norway, where daytime lights were required for motorcyclists prior to the DRL law for passenger vehicles. In the study in Norway, a 4-percent increase, not statistically significant, was found for motorcyclist crashes. In Hansen's evaluation of Denmark's law, daytime multiple-vehicle crashes involving motorcycles were unchanged, but nighttime and single-vehicle daytime motorcycle crashes decreased over this period, leading Hansen to conclude that there might be a "minor negative impact" of DRLs on motorcycle crashes.

Costs of DRLs

One the most foolish arguments raised against DRLs is that they are expensive to implement and decrease fuel economy. This argument is summary dismissed by the facts cited below.

U.S. Department of Health and Human Services, Public Health Reports , Vol. 110 ; No. 3 ; Pg. 233; ISSN: 0033-3549 (May, 1995).
DRL costs are low, so even very modest crash reduction capabilities would be cost effective. For example, according to General Motors, there is a minimal wiring cost in converting to DRLs, and a fraction of a mile fuel penalty (about $ 3 per year for the average driver).


General Arguments critizing the studies

All the good studies that were done were very close to the artic circle. The light conditions there are much different.

All hte safty studies in the US that I have seen tend to compare fleets safty to fleet safty from years ago. These are flawed because the roads are safer now.

A service of the Reasonable Drivers Unanimous home page (

Special thanks to Matthew N. Kleiman <> for a lot of the "Pro" information.

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