When merging onto a freeway, how should you check the lane you intend to enter?

Correct answer: C – Check all mirrors and briefly look over your shoulder
Mirrors do not show every area alongside your vehicle. Check all mirrors, then briefly look over your shoulder to verify that the blind spot is clear before merging. In the District of Columbia, a driver entering a freeway from an access ramp must yield to traffic already on the freeway.
Source: 18 DCMR § 2208.8 – Right-of-Way: Intersections; DC DMV Automobile Driver Manual — “Entering a Freeway” acceptance.

