What does the 'eye lead time' concept refer to in commercial vehicle driving?

EYE LEAD TIME is the practice of continuously scanning the road 12-15 seconds ahead of your vehicle. This is approximately one block in city driving and a quarter mile at highway speeds. WHY 12-15 SECONDS: At 55 mph, a vehicle travels about 80 feet per second. Perception-reaction time (seeing the hazard, deciding to brake, beginning to press the pedal) takes 1.5-2.5 seconds minimum. Braking distance for a loaded truck at 55 mph is approximately 300-400 feet. Total stopping distance therefore exceeds 400 feet. If you're only looking 2-3 seconds ahead (as many drivers instinctively do), you have no time to avoid a hazard — you're already in it. SCANNING TECHNIQUE: Look far ahead for major hazards; scan back to the area 6-8 seconds ahead for developing hazards; check mirrors every 5-8 seconds; use peripheral vision for immediate surroundings. CITY vs HIGHWAY: In the city, 12-15 seconds ahead may be only 1 block — look through and past intersections. On highways, a quarter mile gives you time to anticipate lane changes, merges, and slowdowns well before they become emergencies. MOST SERIOUS HAZARD: Rear-end crashes are the most common type in commercial trucking, and most result from following too closely or not looking far enough ahead.