What is a 'high occupancy vehicle' (HOV) lane?

HOV lanes (also called 'carpool lanes' or 'diamond lanes' from the painted diamond markings) are restricted to vehicles with a specified minimum number of occupants — typically 2+ or 3+ depending on the road and time of day. The restriction usually applies during rush hours; outside posted hours the lane may be open to all traffic. HOV lanes are intended to encourage carpooling and reduce overall congestion. Some HOV lanes accept hybrid and electric vehicles regardless of occupancy under various clean-vehicle programs. Penalties for HOV violations are significant, often $300-$500 in many states. Diamond markings on the pavement and overhead signs identify HOV restrictions.