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For administrative purposes, Caltrans has divided the state of California into districts supervised by district offices. Most districts cover multiple counties; Orange County is the only county with its own dedicated district office. The most important districts are District 4 ( San Francisco Bay Area) and District 7 ( Los Angeles and Ventura counties).
Caltrans has a reputation for being both innovative and stubbornly idiosyncratic. It has long experimented with freeway-to-freeway stack interchanges of increasing height and complexity. It was the last state highway department in the United States to number its freeway exits, and one of the last to switch from dark green "button copy" signs to bright green reflective signs. In the 1990s, Caltrans aggressively added carpool lanes on freeways to reduce traffic congestion.
Although state highways generally adhere to consistent minimum design standards throughout much of the state, there is a strange schism between the Northern and Southern California district offices. Northern California carpoolCarpooling is shared use of a car, in particular for commuting to work, often by people who each have a car but travel together to save costs. There are sometimes special facilities for carpoolers, including high occupancy vehicle lanes specifically for c lanes are always directly adjacent to mainline traffic lanes and are restricted to carpools only during rush hour, while Southern California carpool lanes are always separated from mainline lanes (except at designated entrance/exit areas) and are restricted at all times.