The naming is historical baggage. In practice, "HOV lanes" today serve two (intended) purposes: (1) reduce gridlock; (2) reduce pollution. As originally conceiv

The naming is historical baggage. In practice, "HOV lanes" today serve two (intended) purposes: (1) reduce gridlock; (2) reduce pollution. As originally conceived, (2) could only be achieved by actual high occupancy vehicles being used to reduce the number of vehicles on the road. Now it can also be achieved by low- or zero-emission vehicles, hence the exception.