Efforts to manage transportation demand during rush hour periods vary by state and by metropolitan area. In some states, freeways have designated lanes that become HOV (High-Occupancy Vehicle, aka car-pooling) only during rush hours, while open to all vehicles at other times. In others, such as the Massachusetts portion of I-93, travel is permitted in the breakdown lane during this time. Several states use ramp meters to regulate traffic entering freeways during rush hour. Transportation officials in Colorado and Minnesota have added value pricing to some urban freeways around Denver, the Twin Cities, and Seattle, charging motorists a higher toll during peak periods.