24
HIGHWAY NEEDS OF THE NATIONAL DEFENSE
TUNNELS IN RURAL AREAS
Seven tunnels are in Pennsylvania. They range from 3,512 to 6,792 feet in length, and all provide 23 feet horizontal and 14.3 feet vertical clearance. All are approached by four-lane divided highways, and carried an hourly traffic of 800 to 1,000 vehicles in 1948.
The Mitchell Point tunnel on U S Route 30 in Oregon is so narrow, and its approaches so winding, that traffic-actuated signals were installed to operate the tunnel one way alternately in either direction, Every tunnel on the interstate system is in some degree inadequate in horizontal clearance.
There are four tunnels in Oregon. These vary in length from less than 400 feet to 827 feet, and in width from 16% to 26 feet. Their 1948 hourly traffic was between 260 and 320 vehicles. Vertical clearance on all is 16 feet or more.
