The bridge carries 14 lanes of traffic, seven in each direction. As such, the George Washington Bridge contains more vehicular lanes than any other suspension bridge, and is the world's busiest vehicular bridge. The fourteen lanes of the bridge are split unevenly across two levels: the upper level contains eight lanes while the lower level contains six lanes. The upper level opened in 1931, and is wide. The upper level originally had six lanes, though two more lanes were added in 1946. Although the lower level was part of the original plans for the bridge, it did not open until 1962. The upper level has a vertical clearance of , and all trucks and other oversize vehicles must use the upper level. Trucks are banned from the lower level, which has a clearance of . All lanes on both levels are wide. Vehicles carrying hazardous materials (HAZMATs) are prohibited on the lower level due to its enclosed nature. HAZMAT-carrying vehicles may use the upper level, provided that they conform to strict guidelines as outlined in the Port Authority's "Red Book".