The Eisenhower Tunnel, officially the Eisenhower-Johnson Memorial Tunnel, is a dual-bore, four-lane vehicular tunnel approximately 50 mi (80 km) west of Denver, Colorado, United States. The tunnel carries Interstate 70 under the Continental Divide in the Rocky Mountains. With a maximum elevation of 11,158 ft (3,401 m) above sea level, it is one of the highest vehicular tunnels in the World. The tunnel is the longest mountain tunnel and highest point on the Interstate Highway system.
Completed in 1979, it was one of the last major pieces of the Interstate Highway system to be completed. The westbound bore is named after Dwight D. Eisenhower, the U.S. President for whom the Interstate system is also named. The eastbound bore is named for Edwin C. Johnson, a governor and U.S. Senator who lobbied for an Interstate Highway to be built across Colorado.
Due to additional height restrictions from variable message signs and lighting systems, the original posted clearance of the tunnels was 13.5 feet (4.1 m). The trucking industry lobbied the Colorado Department of Transportation (CDOT) to increase the vertical clearance of the tunnel. With a 2007 retrofit that used lower profile lighting and signs, it is now possible for trucks 13.92 feet (4.24 m) to navigate the tunnel, an increase of 5 inches (13 cm) over the original limit. Sensors will activate audible sirens near each entrance of the tunnel if a vehicle above the posted height attempts to enter the tunnel. Traffic signals at that entrance will turn red, stopping all traffic.
The entrance will remain closed until the over-height vehicle is removed from the freeway, sometimes causing severe delays for all traffic. CDOT noted that prior to the retrofit, about 20,000 vehicles per year tripped the alarm. The trucking industry argued that many of these trucks were under the height requirement but tripped the alarm due to their air suspensions (which can be manually lowered for the duration of the journey through the tunnel) or due to winter snow and ice on top of the trailer. During this time, the trucking industry estimated the number of alarms would drop by as much as 80% if the clearance could be raised even a few inches. Another feature of the retrofit monitors truck weight—a safe speed for each truck on the 7% grades and curves just outside the tunnel is calculated and displayed for each driver.