The tunnel is a two-bore tunnel with each bore approximately 1.7 miles (2.7 km) long. Construction of the westbound bore was started on March 15, 1968 and finished on March 8, 1973. The eastbound bore was started on August 18, 1975 and completed on December 21, 1979. From 1973-79 the westbound bore carried a single lane of traffic in each direction. The total construction cost of the project was $108 million. In 2002, over ten million vehicles passed through the tunnel, many of them driving between the Denver area and popular skiing locations west of the Continental Divide. The eastern end of the tunnel is under and surrounded by the Loveland ski area.
Trucks that cannot safely pass through the tunnel (trucks over 13' 6" (4.1m) in height and trucks carrying hazardous materials), and bicycles and pedestrians, must take the long and steep climb and descent of US 6 across Loveland Pass. Tourists who want to take a photograph from the scenery at an elevation of 11,990 feet (3655 m) above mean sea level must also take Loveland Pass. Aside from that, the tunnel has replaced the pass. Despite being much less formidable than the old route, the approach to the tunnel on both sides is steep (up to 7% in places), and runaway truck ramps are available for truckers who lose control. The tunnel's ascent/descent can also be dangerous in winter.