In jurisdictions where use of headlights is optional when visibility is good, drivers who use headlights at all times are less likely to be involved in a collision than are drivers who use headlights only when visibility is poor. Yet Highway Safety Department records show that making use of headlights mandatory at all times does nothing to reduce the overall number of collisions.
The statement 'A law making use of headlights mandatory at all times is not especially difficult to enforce' most helps to resolve the apparent discrepancy in the information above.