The assured clear distance ahead (ACDA) rule holds the operator of a motor vehicle responsible to avoid collision with any obstacle that might appear in the vehicle's path. Although widely considered a fundamental responsibility of safe driving, the ACDA rule is routinely violated by most drivers under nighttime conditions. This fact does not necessarily imply reckless disregard for public safety, however. Rather the troublesome discrepancy between drivers' behavior and the principles of safe driving may be understood in terms of vehicle operators' lack of awareness of selective losses of visual function that occur in low light. This theoretical perspective holds basic implications both for traffic regulations and for assessment of liability in nighttime road accidents.