Headlights make night driving possible, especially on unlit roads, but they aren't perfect.
A study conducted by engineers at the Automotive Research Center and the AAA National Office found that many headlights may not provide adequate illumination when driving at higher speeds—or, in some cases, speeds as low as 40 mph.
The reasons for this include variations in power between types of headlights, deterioration of older headlight housings, and the need to prevent glare from affecting oncoming traffic. Headlight shortcomings have serious implications: Only 25% of driving takes place in darkness, but 50% of crashes occur in that same period. Drivers should ensure that their headlights are in good working order, and that they understand their headlights' limitations.