Nighttime collision rates per mile are 19% lower for vehicles with headlights that earn a good rating from the Insurance Institute for Highway Safety, compared with those with poor-rated headlights, according to a recent study conducted by IIHS research engineers.

Even vehicles that scored just acceptable or marginal headlight ratings from IIHS reduced the dangers of night driving — with crash rates 15% and 10% lower, respectively, than those with poor ratings.

The first study to document how much headlights that provide better illumination can curb crashes after dark, the study findings also indicate that crash reductions were greater for specific types of collisions.

For example, compared with poor headlights, good-rated headlights reduced the rate of crashes in which the driver was injured by 29% and the rates of tow-away crashes and pedestrian crashes by about 25% each.

The overall goal of the research was to evaluate whether or not IIHS’ headlight rating program is making a difference in the real world.  The results indicate that the IIHS program — established in 2016 — is working, with headlight tests translating into safer nighttime driving on the nation’s roads.

IIHS points out that federal headlight regulations, which have not changed significantly since 1968, are not stringent enough.

IIHS uses vehicles driven on a test track to conduct its evaluations. The ratings are based on how far the low and high beams illuminate the path to 5 lux on curves and straightaways while traveling at 40-50 MPH. Points are also deducted for glare that can temporarily blind oncoming drivers. For reference, the end of twilight on a clear day is about 3 lux and the ambient light in the hallway of a typical office building is about 80.

Performance varies greatly. The low-beam illumination of headlights evaluated by IIHS ranges from 125 feet to 460 feet. For the driver of a vehicle going 50 MPH, that means a difference of 2 seconds versus 6 seconds to recognize a potential hazard and respond by braking or steering.

Since the IIHS program launched, the proportion of headlights earning a good rating has increased from 4% to 29%. Irrespective of their ratings, the average low-beam illumination distance for all the headlights tested rose from less than 180 feet to more than 200 feet.

Moreover, excessive glare is less of an issue than it was five years ago. In 2016, the headlight systems rated by IIHS emitted 15% more glare on average than the level IIHS determined to be acceptable. In 2020, average glare was 10% below that threshold.