While the conclusion should come as no surprise (better lighting = fewer crashes), senior research engineer Matthew Brumbelow said this study is the first-of-its-kind to document real world results—validating that better headlight scores (and better illumination) translate into safer nighttime driving. From a pool of 187 vehicle models from model years 2015-20, the study examined police accident reports from 11 states. After isolating almost 44,000 single-vehicle crashes that happened in darkness, Brumbelow adjusted the ratings to exclude any point deductions for excessive glare because it is not a factor in single-vehicle crashes.

Key findings from the study reveal:

• On-road illumination provided by vehicle lights varies widely.
• Nighttime crash rates per mile are almost 20% lower for vehicles with headlights that earn a good rating in the IIHS evaluation, compared with those with poor-rated headlights.
• Compared with poor ones, 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.
• Among different components of the IIHS rating, the assessments of low- and high-beam curve visibility were associated with the greatest crash rate reductions.

Since the IIHS rating program began, the proportion of headlights earning a good rating has increased from 4% to 29%. The organization is hopeful that results from this study will further incentivize automakers to advance their headlight designs to reduce the risk of nighttime crashes even more. For more information about the study and its methodology, visit the IIHS website.