What is 'overdriving your headlights' and why is it dangerous?

OVERDRIVING HEADLIGHTS means traveling at a speed where your stopping distance EXCEEDS your headlight sight distance — so if a hazard appears at the edge of what your headlights illuminate, you physically cannot stop before reaching it. THE MATH: Low beam headlights illuminate approximately 250 feet ahead. At 55 mph, a loaded truck's minimum stopping distance is 300-400 feet. Result: even at moderate highway speeds, a loaded truck CANNOT stop within low-beam headlight range if a stationary obstacle appears at the limit of visibility. This is why night driving requires reduced speed or the use of high beams (when appropriate). HIGH BEAMS: illuminate approximately 400-500 feet; must be switched to low beams within 500 feet of an oncoming vehicle or 300 feet when following a vehicle; high beams help reduce the overdriving problem. ADDITIONAL NIGHT HAZARDS: Impaired and fatigued drivers are much more common at night; pedestrians and cyclists are harder to see; animals are more active; fatigue is a greater personal risk at night (circadian rhythm). ADJUSTMENTS FOR NIGHT DRIVING: Reduce speed to match sight distance; increase following distance (other drivers' brake lights are your warning — you need time to react); ensure all lights are working during pre-trip; clean lights and mirrors before night driving; keep windshield clean (glare from oncoming headlights is worse on a dirty windshield).