How High Does the US Interstate Highway System Go?

Of the more than 41,000 miles (65,983 km) of road making up the US Interstate Highway System, the highest lanes travel about 1.7 miles (2.7 km) through the Rocky Mountains, taking Interstate 70 across the Continental Divide an hour west of Denver, Colorado. The tunnel, named for President Dwight D. Eisenhower, was finished in 1979 at an elevation of 11,158 feet (3,401 m).

One of the last major pieces of the system to be completed, the Eisenhower Tunnel bypasses Loveland Pass, relieving drivers of the chore of crossing the divide along old US Highway 6, with its treacherous hairpin turns.

The world's longest mountain tunnel:

• The Eisenhower Tunnel used to be the world’s highest tunnel. It has since been eclipsed by Fenguoshan Suidao, a 16,000-foot (4,877 m) tunnel in Tibet. The Eisenhower Tunnel is still the longest mountain tunnel.
• The original clearance of the tunnels was 13.5 feet (4.1 m), but the trucking industry persuaded engineers to modify lighting and signs in 2007 to increase it by 5 inches (12.7 cm). Sensors trip sirens near each entrance if a vehicle above the posted height limit attempts to enter.
• During construction, fault lines were discovered, and cave-ins began to endanger workers on the project. Despite safety precautions, seven workers died building the tunnel.