The parking structure at San Francisco International Airport (SFO) was completed by Dreyfuss + Blackford in 1981, in a joint venture with John Carl Warnecke and Associates. It provides parking for 7,000 automobiles on five levels. Enclosed bridges – with moving sidewalks – provide primary access to the terminals and boarding areas. A second connection between parking and terminals is provided at the first level by tunnels. The entrance plaza to the structure contains five lanes and direct ramps to each of the five parking levels. An electronic control system is provided to guide drivers, via red and green lights and changeable message signs, to an available parking stall. Exit toll booths are also at each of the levels. Up and down ramps, surrounding a landscaped central open space 200 feet in diameter, provide for easy inter-floor circulation.