In an effort to ease traffic density, some metropolitan areas or states implemented HOV lanes or constructed HOV roadways. These stretches of highway are generally restricted in use to vehicles with two or more passengers. In most locales, these restrictions only apply during the peak hours of traffic. However in some cities, the HOV restriction is in place 24 hours. Variable message signs indicate the restriction times and changes. Interstate 66 between Washington D.C. and the Capital Beltway was once completely signed as HOV-4. That meant that anyone driving on any lane of the Interstate with less than four passengers (driver include) would be in violation. Many HOV facilities were converted to High Occupancy Toll (HO/T) or Express toll lanes.