Interstate 70 through the Rocky Mountain front range is a major highway carrying commerce and passengers of all varieties. It is the main truck route for goods to Summit County and towns on the West Slope. It is also a main east-west throughway for long haul trucks that just pass through Colorado.
I-70 also serves the many Colorado Ski Resorts including Vail, Aspen, Winter Park, Keystone, Breckenridge and others. Weekend ski traffic is very heavy in both directions. In the summer I-70 is also the gateway into the Rocky Mountains for campers, bikers, hikers, climbers, kayakers, floaters and many recreational users. Summer recreational traffic is actually higher than winter ski traffic although spread out more.
Much of I-70 cuts through narrow valleys where there is little room to add a single additional lane. Even where lanes can be added the cost is high and there are serious rockslide issues from extreme slopes. The mountain pass is also steep with 7 and 8 percent grades and truck run away lanes. Winter weather on I-70 can be extremely challenging with frequent snowfall and sudden blizzards. The pass is usually shut down several times a year. Severe weather slows traffic, increases the risk of accidents.
There are also several short tunnels and the long Eisenhower Tunnel over the continental divide. The very existence of tunnels slows traffic.