[4] Due to additional height restrictions from variable-message signs and lighting systems, the original posted clearance of the tunnels was 13 ft 6 in (4.11 m).

[1] The trucking industry lobbied the Colorado Department of Transportation (CDOT) to increase the vertical clearance.

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.

[6] The 2007 retrofit also added a weigh-in-motion system that calculates a safe speed for trucks on the 7% grades and curves on the departures from the tunnels and displays it to each driver.

And while the tunnel's route is less formidable than the pass, its approaches are steep nonetheless and have runaway truck ramps.

Engineers recommended tunneling under the pass, rather than attempt to build a route across conforming to Interstate Highway standards.

[13] One of the biggest setbacks was the discovery of fault lines in the path of the tunnel that were not discovered during the pilot bores.

[16] These faults began to slip during construction and emergency measures had to be taken to protect the tunnels and workers from cave-ins and collapses.

[17] Further complicating construction, the boring machines could not work as fast as expected at such high elevations and so the productivity was significantly less than planned.

"[15] Though the project was supposed to take three years, the tunnel was not opened to traffic until a March 8, 1973, dedication ceremony by Governor John Love.

The amount of traffic through the tunnel exceeded predictions, and efforts soon began to expedite construction on the southern bore.

When Janet Bonnema applied for a position as an engineering technician with the Colorado Department of Transportation she was given an assignment on the Straight Creek Tunnels project.

Emboldened by the passage of an equal rights law in Colorado, she finally entered the tunnel, with an entourage of reporters, on November 9, 1972.

[24] A Martin 4-0-4 charter aircraft, one of two carrying the college football team of Wichita State University, crashed just north of the highway (39°41′37″N 105°52′57″W / 39.6935°N 105.8825°W / 39.6935; -105.8825).

[25] The team was on its way to a game with Utah State University in Logan and had recently refueled at Denver's Stapleton International Airport.

The plane carrying the team's starters departed Denver and traveled a poorly planned scenic route.