Estimated potential of human drivers and automatic braking to prevent frontal crashes based on headlight visibility.

Objective: In 2021; half of crash fatalities occurred at night when some road users, like pedestrians, are particularly vulnerable. Automatic emergency braking (AEB) systems can avoid or mitigate collisions by automatically applying the brakes, but their performance may be hindered in low lighting. The purpose of this study was to estimate the proportion of real-world crashes where headlights could provide enough visibility for the driver or AEB system to detect and avoid the collision.

Methods: This study used IIHS headlight testing data and Crash Report Sampling System crash data from 2016 to 2021. The median 5-lux visibility distance was calculated for each IIHS headlight rating: good, acceptable, marginal, and poor. For three response profiles, a typical human driver, a fast human driver, and a camera-based AEB system, the maximum travel speed in which a vehicle could come to a complete stop within the 5-lux distance was computed. The real-world crash coverage of each headlight system and response profile was defined as the proportion of crashes that occurred on dark, unlit roads with a speed limit below the estimated maximum travel speed, where the vehicle could stop within the visibility distance.

Results: The median low-beam visibility distance for poor-rated headlights was 68.2 m and for good-rated headlights was 103.1 m on the right side of straight roads. The typical human driver could have enough time to detect and avoid 46.2% of nighttime pedestrian crashes with poor-rated headlights and 70.1% with good-rated headlights. The visibility distance greatly increases with high beams and would allow the typical human driver to detect and avoid over 90% of nighttime crashes. Good-rated and acceptable-rated headlights allow AEB systems to theoretically have enough visibility distance to avoid nearly every nighttime crash.

Conclusions: Vehicles with good- or acceptable-rated headlights and active high beams are theoretically capable of providing sufficient light for speeds up to 165.8 km/h (103 mph), even covering most speeding vehicles. Future simulations of AEB systems on vehicles equipped with good- or acceptable-rated headlights and automatic high beams may not need to consider headlight visibility.