Reaching an elevation of 11,158 feet above sea-level, Colorado’s Eisenhower Tunnel is both the longest mountain tunnel and the highest point in the United States’ interstate network. It’s also the highest vehicular tunnel in the world.

Though drilling of this iconic feature of Interstate 70 started in 1968, the ideation of the tunnel dates back to the 1950s with talk about building a route beneath Loveland Pass. When it was eventually decided to build an interstate route across Colorado, politics (in short) determined that the best route would be along the US 6 corridor and engineers determined that the route should travel beneath the Continental Divide instead of over it.

Stretching approximately 1.69 miles long, it would be 1973 when the westbound “bore” opened and 1979 when the ribbon was cut for its eastbound equivalent. Upon its competition, the route would save drivers traveling the state roughly 9 miles and the hazards of having to travel a very exposed Loveland Pass.

Not to surprise, building a tunnel this large under a mountainside was a dangerous task. It was so dangerous that some accounts report that seven workers were killed throughout the construction. Many others are said to have faced serious injuries on the job.

According to the Denver Post, the total cost of the construction was $262 million. Adjusted for inflation, that would be around $1.5 billion dollars today. That’s not too shocking given that parts of the tunnel are roughly 1,500 feet beneath the surface.

The tunnel is officially called the Eisenhower–Edwin C. Johnson Memorial Tunnel, with the westbound bore named for Dwight D. Eisenhower’s role in the development of the interstate system and the eastbound bore being named for Edwin C. Johnson’s role in making Colorado’s I-70 route a reality. Johnson served as governor of Colorado and in the U.S. Senate.

Today, the tunnels are still staffed 24 hours a day with a 52 person full-time staff, said by some to cost more than $1,000 a day to maintain.

An iconic landmark for those headed to ski country, Eisenhower Tunnel’s reliable access to Summit County can get crowded at times, but it gets the job done, serving more than 13 million drivers a year and an average of roughly 37,000 per day. Imagine if that much traffic was still solely relying on the two-laned Loveland Pass.

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