584 AISTJTUAL REPOKT SMITHSONIAN INSTITUTION, 19 3 



In considering the requirements for the width of the roadways 

 and the clear headroom needed, measurements were taken of vehicles 

 crossing the Hudson on the ferries between New York and New 

 Jersey. It was found that their height varied from 6 feet 6 inches 

 for passenger cars to a maximum of 13 feet for large loaded trucks, 

 but that the number exceeding 12 feet in height was only 1 per cent. 

 The width of motor vehicles varied from 6 feet for passenger cars 

 and light trucks to a maximum of 10 feet 6 inches for army transport 

 trucks. In the case of 3-horse teams, the outside dimension of the 

 three horses abreast was 9 feet, but the number of vehicles exceeding 

 8 feet in width was only 3i/^ per cent. 



In determining the amount of clear headroom required, it was 

 necessary to consider the matter of providing sufficient area in the 

 tunnel roadway. Any increase in clear headroom, without increas- 

 ing the size of the tunnel, could be made only at the expense of the 

 available ventilating duct area. Any reduction in this area would 

 increase the power required for ventilation and add to the cost of 

 operating the tunnel. 



Given a maximum height of 12 feet 2 inches and a maximum width 

 of 8 feet, a clear headroom of 13 feet 6 inches seemed adequate to 

 allow even for jacking up vehicles in case of breakdown, and this 

 was decided upon. 



Normal operating conditions in a tunnel accommodating two 

 lines of vehicles in the same direction on one roadway obtain when 

 there is a slow line of heavy trucks 8 feet wide abreast of a fast line 

 of light trucks and passenger cars 6 feet wide. It is, however, 

 necessary to provide for such a contingency as when a vehicle of 

 maximum width has to pass another of the same width that has 

 stalled. The roadway has to be sufficiently wide to permit the pas- 

 sage abreast of two vehicles of maximum width. 



It was believed that in the slow line, operating at a speed varying 

 from 3 to 6 miles per hour, a clearance of not less than 6 inches 

 between the outside of the tire and the curb should be provided. In 

 the fast line, due to the greater speed, this clearance should not be 

 less than 1 foot. It was also considered that for safe and convenient 

 operation a clearance between moving vehicles of 2 feet 9 inches 

 should be allowed. These considerations led to the adoption of a 

 width of roadway of 20 feet, with, in addition, a sidewalk 2 feet 

 wide in each tunnel. This sidewalk is set back from the curb line 

 a distance of 6 inches and is located at an elevation of 26 inches 

 above the roadway. 



This roadway is paved with granite blocks laid in the usual sand 

 cement cushion layer, about 1 inch thick, with the joints filled with 

 hot asphalt mixed with heated sand. By means of squeegees, a thin 

 coating, sprinkled with sand, is left upoii the surface, resulting in a 



