When is it appropriate to sound the horn while driving a CMV?

The HORN is a critical communication tool for CMV drivers and should be used proactively, not reactively. Commercial vehicles have significant blind spots — the right side, the immediate front, and the rear — that make it impossible for nearby road users to always see you.

Appropriate horn use: (1) APPROACHING INTERSECTIONS with limited visibility (blind corners, buildings at the corner blocking sight lines) — a brief horn tap warns pedestrians and turning vehicles; (2) WHEN A NEARBY VEHICLE appears not to see you and is drifting toward you — a horn blast can prevent a merge collision; (3) WHEN PASSING CYCLISTS or pedestrians in areas where your approach might not be heard — a soft tap 100+ feet before you pass; (4) WHEN YOUR LIGHTS AND SIGNALS DON'T COMMUNICATE your intention — unusual maneuvers or emergency situations; (5) TO WAKE UP A DRIVER at a green light who hasn't moved (use sparingly).

What the horn is not: Not a tool for expressing frustration (road rage); not a way to signal someone you're behind them to go faster; not for casual greetings except in light traffic.

Federal requirement: CMVs must be equipped with a functional horn per FMCSA regulations (49 CFR 393.81). The horn is checked during pre-trip inspection.