High Occupancy Vehicle Lanes are supposed to reduce pollution via ridesharing, and are better known as Carpool Lanes. These are found on many freeways, although many older freeways have not yet incorporated them in certain portions yet. They often have a minimum passenger requirement of 2, though previously the standard was around 3-4 (At least in Los Angeles).
An good example of bad carpool lane design is that of Interstate 10 eastbound from around Interstate 710 to the Baldwin Avenue exit, the 30+ year old El Monte Busway. There is only 1 entrance in the approximately 11 miles of its length making this carpool mostly useless. Many people illegally enter here and get ticketed.
Message to CalTrans: FIX THIS! YOU ENCOURAGE PEOPLE TO USE CARPOOL LANES!