Nighttime visibility is critical to highway safety. About half of traffic deaths occur either in the dark or at dawn or dusk. Better headlights lead to fewer nighttime crashes.
Not all headlights do their job well. IIHS evaluations show that the on-road illumination provided by vehicle lights varies widely.
Good headlights shouldn't cause excessive glare. Properly aimed low beams light up the road ahead without temporarily blinding drivers of oncoming vehicles. IIHS headlight ratings take glare into account.
Some new types of lighting technology are helping. High-beam assist, curve-adaptive headlights and, more recently, adaptive driving beams all improve on-road visibility.