About the Eisenhower Tunnel
The Eisenhower Memorial Tunnel, about 60 miles west of Denver on Interstate 70, is the highest vehicular tunnel in the world—at an elevation of 11,013 feet at the East Portal and 11,158 feet at the West Portal. The Tunnel traverses through the Continental Divide at an average elevation of 11,112 feet.
The facility lies entirely within the Arapaho National Forest and is divided by two counties: Clear Creek County at the East Portal and Summit county at the West Portal. The Tunnel and the Continental Divide also separate two watersheds: the Clear Creek Watershed on the east side and the Straight Creek Watershed on the west side. Annual snowfall in the area averages 315 inches (26 feet) from November through April.
The Tunnel was originally designed as a twin bore tunnel. Construction on the westbound bore (North Tunnel) began March 15, 1968, and was completed five years later on March 8, 1973. This bore was originally called the Straight Creek Tunnel, and later was officially named the Eisenhower Memorial Bore.
Construction on the second bore began Aug. 18, 1975, and was completed four years later on Dec. 21, 1979. This eastbound bore was named after Edwin C. Johnson, a past governor and U.S. senator who had actively supported an interstate highway system across Colorado.
Centerline to centerline, the two tunnels are approximately 115 feet apart at the east ventilation building entrance, 120 feet apart at the west ventilation building entrance, and some 230 feet at the widest point of separation under the mountain.
The length of the westbound (north) tunnel is 1.693 miles, and the length of the eastbound (south) tunnel is 1.697 miles (outside, face to outside face of the ventilation buildings).
The average grade of both tunnels is 1.64 percent rising toward the west (rising 1.64 feet for each 100 feet on the horizontal). The westbound tunnel curves slightly to the left, about midway into the mountain. The approach grades are steep, being 7 percent on the west approach and 6 percent on the east approach.
Maximum excavated height for the tunnels is 48 feet, with a width of 40 feet. However, when driving through the tunnels, the actual height is not apparent. The exhaust and supply air ducts are above a suspended porcelain enamel panel ceiling, and a drainage system is provided underneath the roadway surface.
Today, the driver sees only the distance (vertical clearance) from the roadway surface to the ceilings in the tunnels—a distance of 16 feet, 4 inches. However, because of a series of variable message boards mounted from the ceiling, actual clearance is set at 13 feet, 11 inches. The width in both bores provides two traffic lanes of 13 feet each, providing a total travel width of 26 feet. Tunnel maintenance personnel utilize a walkway that runs adjacent to the vehicle travel lanes. The walkway also provides access between the westbound or eastbound tunnels through three cross passageways, which are spaced at 2,000-foot intervals.
The tunnel is staffed 24 hours a day, 365 days a year, in order to provide a safe and adequate level of service to the motoring public. The current staffing level is set at 52 full-time employees.