Hanging Lake Viaduct carries I-70 along the Colorado River through an extremely steep and narrow portion of the environmentally sensitive Glenwood Canyon. In addition to providing a design that would protect the environment, traffic flow had to be maintained during construction. The bridges were built using precast concrete segmental box girders, which met the project requirements for overhead erection, aesthetics, and schedule. The eastbound structure is 1,308’, and the westbound structure follows the steep, rocky slopes for 7,121’. Both bridges emerge from twin tunnel portals and cross the Colorado River with 300’ spans.