March 2016

  1. Do all headlights sold today provide enough light?

    No. Although data about the on-road performance of headlights is limited, IIHS ratings show that visibility provided by headlights varies widely. The Institute released its first headlight ratings in 2016. Out of more than 80 headlight systems available on 31 midsize cars that were evaluated, only one system received a good rating. More than half were rated poor because of inadequate visibility, excessive glare from low beams for oncoming drivers, or both.

    It takes 1.5 seconds for a driver to react to an unexpected event under ideal conditions. Green, M. 2000. "How long does it take to stop?" Methodological analysis of driver perception-brake times. Transp.Human Factors 2(3): 195-216. At a speed of 55 mph, a car travels about 120 feet during this brief period. Once the driver applies the brakes, it takes more than 144 feet, on average, to stop at this speed. Jernigan, J.D. and Kodaman, M.F. 2001. An investigation of the utility and accuracy of the table of speed and stopping distances specified in the Code of Virginia. Final Report. Report no. VTRC 01-R13. Charlottesville, VA: Virginia Transportation Research Council. Given these distances, 42 percent of the low-beam headlight systems the Institute tested don't provide enough light for a driver going 55 mph on a straight road to stop in time after spotting an obstacle in his or her lane. It's important to note that low beams provide even less illumination on the left side of a straight road and when driving on a curve.

  2. Does the U.S. government regulate headlights?

    There are federal regulations on headlights, but headlights that meet the regulations don't necessarily have similar on-road performance. Under the standard, a headlamp is placed on a test rig, and light intensity is measured at different angles relative to the center of the lamp. Measurements are taken for visibility and glare, but the standard permits a large range of intensities and the angles can be adjusted within a relatively large tolerance. In addition, once the headlights are put on a vehicle, the regulations allow a wide range of mounting heights and widths and don't say how they should be aimed. As a result, two vehicles could be equipped with the same headlights but have a large difference in the distances illuminated.

    One clear requirement is the need for all vehicles to have separate low-beam and high-beam headlights. The requirement is intended to provide maximum visibility with high-beam headlights when drivers are on unlit roads without other traffic around and to provide sufficient low-beam visibility while limiting glare exposure when oncoming or leading vehicles are near.

  3. What technological innovations have been made in vehicle lighting?

    Between 1940 and the mid-1980s, almost every vehicle in the United States was sold with standardized sealed-beam glass headlamps. Moore, D.W. 1998. Headlamp history and harmonization. Report no. UMTRI-98-21. Ann Arbor, MI: University of Michigan Transportation Research Institute. Beginning in the 1970s, these were filled with halogen gas to improve performance. Since the mid-1980s, most vehicle models have had customized headlights with replaceable bulbs. Halogen bulbs now have competition from LED and high-intensity discharge (HID) lamps. These newer light sources are more efficient than halogen bulbs (and LEDs are much more efficient than HIDs), so they can produce more light with the same amount of energy. They also produce light with a more natural color than halogen bulbs.

    Many of today's vehicles are available with curve-adaptive headlights. These headlights pivot in the direction of travel based on steering wheel movement and sometimes the vehicle's speed to illuminate the road ahead. They are intended to make it easier to see on dark, curved roads.

    Another increasingly common feature is high beam assist. This technology uses a camera to automatically switch between high beams and low beams, depending on whether other vehicles are present. The driver still has the option to manually switch between low and high beams.

    Headlights with an adaptive driving beam, not to be confused with curve-adaptive headlights, are similar to high beam assist. However, instead of switching the high beams on and off, they continuously adjust the high-beam pattern to create a shadow around other vehicles. In this way, adaptive driving beams offer high-beam visibility except for the segment of the beam that is blocked out to limit glare for oncoming or lead drivers.

    Adaptive driving beams are currently prohibited in the United States because the regulations require separate high- and low-beam systems. The Society of Automotive Engineers plans to publish recommendations for test procedures, performance requirements, and design and installation guidelines for adaptive driving beams to facilitate the revision of federal safety standards to allow this technology.

  4. Do these innovations improve safety?

    Studies show that curve-adaptive headlights reduce crashes, though it can be hard to tease out how much of the benefit is from HID or LED lamps and how much is from curve adaptivity.

    HLDI studied curve-adaptive headlights offered by Acura, Mazda, Mercedes and Volvo and found that claim rates generally fell. Highway Loss Data Institute. 2013. Acura collision avoidance features – an update. HLDI Bulletin 30(15). Highway Loss Data Institute. 2015. Mazda collision avoidance features. HLDI Bulletin 32(22). Highway Loss Data Institute. 2012. Mercedes-Benz collision avoidance features: initial results. HLDI Bulletin 29(7). Highway Loss Data Institute. 2012. Volvo collision avoidance features: initial results. HLDI Bulletin 29(5). The effect was particularly consistent for claims under property damage liability coverage, which pays for damage to other vehicles and property, where rates fell as much as 9 percent.

    The reduction of property damage liability claim rates was surprising, since only about 13 percent of police-reported crashes occur on dark roads and involve more than one vehicle. An even smaller percentage are multiple-vehicle, nighttime crashes occurring on a curve, where curve-adaptive headlights would be expected to have the most effect. It's possible that other differences between the curve-adaptive headlights and conventional ones besides steerability may have played a role in reducing crashes with other vehicles. Curve-adaptive headlights usually have LED or HID lamps, while fixed lights can be LED, HID or halogen.

    In an experimental study with volunteers driving a vehicle with three different lighting systems, curve-adaptive high-intensity discharge (HID) headlights allowed drivers to spot a hard-to-see object on a dark, curvy road about one-third second earlier than with conventional fixed headlights. Reagan, I.J.; Brumbelow, M.L.; and Frischmann, T. 2015. On-road experiment to assess drivers' detection of roadside targets as a function of headlight system, target placement, and target reflectance. Accident Analysis and Prevention 76:74-82.

    High beam assist is not yet widespread enough to determine if it reduces crashes, but researchers from IIHS and the University of Michigan Transportation Research Institute found that drivers in and around Ann Arbor, Mich., didn't use their high beams enough. Reagan, I.J.; Brumbelow, M.J.; and Flannagan, M.J. 2016. The effects of rurality, proximity to other traffic, and roadway curvature on high beam headlamp use rates. Arlington, VA: Insurance Institute for Highway Safety. Only 18 percent of drivers who were isolated enough to make use of their high beams did so. High beam assist could improve this rate if drivers are simply forgetting to turn on their high beams, are unsure whether oncoming vehicles are far enough away to do so safely, or understate the effects of high beams on safety.

  5. Don't headlights that provide more light cause glare for drivers of other vehicles?

    Not necessarily. Properly aimed headlights can illuminate the road ahead without getting in other drivers' eyes. Many people encounter blue-colored headlights that cause disturbing glare, but these often are the result of illegal aftermarket HID conversion kits. Specialty Equipment Market Association. 2007. Government clamps down on HID conversion kits. SEMA eNews 10(18). Diamond Bar, CA.

  6. Where can I get information about headlight performance?

    IIHS began publishing headlight ratings in 2016, beginning with midsize luxury and nonluxury cars. Several different headlight combinations may be available on a single model, and the Institute tries to test all of them, as they become available from dealers.

    Each rating provides information on the amount of visibility provided by low beams and high beams as a vehicle travels straight and on curves, and whether the glare produced for other drivers is excessive. Credit is also given for vehicles that have high beam assist.

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

    Daytime running lights (DRLs) are low-intensity 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 for vehicles to be seen, particularly as they approach from far away or in inclement weather.

    Laws in Canada and many European countries require cars, trucks and buses to operate with lights on during the daytime. These requirements began in 1989 for Canada and in 2011 for the European Union. No U.S. state mandates DRLs, but some require drivers to operate vehicles with lights on in bad weather.

    In the U.S., DRLs were first offered on a handful of 1995 passenger vehicles. Since then, they have become quite common. DRLs are standard on all General Motors, Honda, Subaru, Volkswagen and Volvo models. Other manufacturers also offer daytime running lights on certain models. Retrofit kits can be purchased for vehicles that didn't come with DRLs.

  8. How effective are DRLs?

    Nearly all published reports indicate DRLs reduce multiple-vehicle daytime crashes. 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. 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 multiple-vehicle daytime 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. 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 reduce crash involvements of pickups, SUVs and vans but have no significant effect on crashes of passenger cars. 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.