More than 434 million vehicles have traveled through the I

Clear Creek County - Fifty years ago today, the 1.7-mile long I-70 Eisenhower Tunnel opened to traffic. Located about 60 miles west of Denver and under the Continental Divide, the tunnel has served as a vital transportation connector for the state and the interstate system.

The Colorado Department of Transportation marked the historic milestone by pausing westbound traffic for 50 seconds, so the Colorado State Patrol's vintage 1970 Fury was the first vehicle to usher in the tunnel's next half-century. It was a state patrol vehicle that first entered the tunnel when it opened to traffic 50 years ago. As of 11 a.m. today, exactly 434,431,100 vehicles traveled through both the Eisenhower and Johnson Memorial Tunnels since March 8, 1973.

Today, the Colorado State Patrol vehicle was followed by a vintage 1970's vehicle and CDOT's tunnel fire truck.

The Eisenhower Tunnel is the highest point on the nation's interstate system at 11,200 feet. At one time, the Eisenhower Tunnel was the highest vehicular tunnel in the world. It originally served both east and westbound traffic. When the Johnson bore was completed in 1979, eastbound traffic shifted to its own two-lane tunnel.

"While motorists drive through the tunnel in a few minutes, they may not realize the monumental effort it took to plan and build such an infrastructure under the most challenging of circumstances," said CDOT Executive Director Shoshana Lew. "Over a five year construction period, 6,000 people and heavy machinery worked a total of 4.9 million hours to bore through granite under the Continental Divide in harsh weather conditions. When construction started in 1968, it was the largest single federal-aid highway project in the nation's history. For the last five decades, the Eisenhower Tunnel has served as the great connector, tying east and west Colorado together. It has provided a critical life-saving link for moving goods and services and helped to mark Colorado as a world-class mountain destination."

Before the tunnel was built, the east-west mountain routes in Colorado were US 6 over Loveland Pass and US 40 over Berthoud Pass. Those passes can be treacherous during the winter, greatly limiting travel. Once the interstate system was taking shape across the country in the 1960s and 70s, the Eisenhower Tunnel became one of the crown jewels of the west, providing a safer and more efficient route through a mountain instead of over it.

There were monumental obstacles to building the tunnel. Crews worked in brutal winters at over 11,000 feet, and then new engineering methods were needed to shore unstable rock so a hole 50 feet high and 45 feet wide could be supported. What was expected to take three years to build took five years, and at a cost of $110 million. As one veteran highway engineer put it, "We were going by the book, but the damned mountain couldn't read." One federal highway engineer stated in the Denver Post in 1972, the project involved "pioneering every foot of the way."

Photos of crews working in the Eisenhower Tunnel while it was under construction in the late 1960's.

No women worked in the tunnel because many of the miners warned if a woman entered a mine or tunnel, she would cause a fatal accident. That all changed in 1972 when 33-year-old Janet Bonnema qualified for a job to work in the tunnel. She took the highway department to task when they wouldn't allow her to set foot in the tunnel because of her gender. Bonnema filed a sexual discrimination lawsuit against the Department of Highways but eventually settled out of court. She later reported to work in the tunnel. But when she showed up for work, over 60 tunnel workers walked off the job in protest, but soon returned.

A dedicated crew of more than 30 full-time employees work at the tunnel facility with job duties ranging from round the clock television surveillance, emergency response, tunnel washing, ventilation maintenance, tunnel sweeping, snow removal, heavy equipment servicing and repair, and water treatment. The CDOT tunnel crew also serves as firefighters complete with fire trucks and firefighting equipment to respond immediately to incidents. A new tunnel fire suppression system was built in 2015.

Safety is the most critical priority for tunnel operations. There have been no fatalities in either bore.

An average of 35,000 vehicles a day travel the tunnel, with the highest volumes of over 50,000 a day typically in July and August.

CDOT is modernizing much of the tunnel's internal operations systems (electrical, water treatment plant and other functions) and continues to upgrade outdated and aging infrastructure. These projects are part of CDOT's 10-Year Plan, with funding made possible through Senate Bill 260 and the Bridge & Tunnel Enterprise.

For more information about the Eisenhower Tunnel, visit:

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