"High occupancy vehicle" lanes, popularly known as carpool or HOV lanes, are highway lanes reserved for vehicles carrying two or more people. Their purpose is to ease highway congestion, especially in large urban areas. California has numerous carpool lanes throughout the state and using them can relieve much of the stress that often comes with driving in bumper-to-bumper traffic. But first, make sure you're authorized to do so by having the proper vehicle or right number of passengers inside.