When you switch from high beams to low beams at night, how should you adjust your speed?
Correct answer: B – Slow down as necessary to remain within your sight distance
Low beams normally illuminate about 250 feet ahead, while high beams illuminate approximately 350 to 500 feet. When the visible distance decreases, the driver should reduce speed as necessary. Your stopping distance must remain within the distance you can see, allowing you to stop before reaching a newly visible hazard.
Source: Massachusetts Commercial Driver’s License Manual — § 2.11.4, “Vehicle Factors”

