In order to better utilize available capacity in high-occupancy vehicle (HOV) lanes, states are permitted to allow certain qualifying non-HOVs to use HOV lanes. In general, states may allow motorcycles, public transportation vehicles, high-occupancy toll (HOT) vehicles, and low-emission and energy-efficient vehicles to use HOV lanes. For any or all of these types of vehicles, the states must establish programs addressing candidacy, enrollment, and management of the lanes. In the case of tolled vehicles, dynamic pricing is the primary control that limits the potential to cause congestion in the lanes. In the case of the energy-efficient vehicles, the programs typically include decals, licenses, license plates, or stickers, that serve to identify and, in some cases, cap the number of allowed to use the lanes vehicles. Concerns may arise that the number of exempted vehicles may overburden the capacity of the HOV lanes to perform their primary function, which is to provide an incentive to form carpools (and thereby reduce the number of cars on the road) and to "reward" such an incentive by guaranteeing a mostly delay-free trip. Use by non-HOVs may overburden the HOV lanes, causing the integrity of the HOV lanes to suffer. The Moving Ahead for Progress in the 21st Century Act (MAP-21) 2012 now mandates that any HOV facility that allows tolled vehicles or any class of qualifying energy-efficient vehicles must annually certify that the subject lanes are "not degraded." By definition, this constitutes that for a 180-day continuous reporting period, the lane(s) operate at greater than 45 mph for 90% of the time. (See Section 166, Title 23 of United States Code for the full language.) This report examines programs in use by states allowing low-emission and energy efficient vehicles to use HOV, HOT, and managed lanes without meeting the vehicle-occupancy requirements. Information is presented on the enabling legislation, the program elements, use of the programs, and impacts of the HOV, HOT, and managed lanes in 13 states.