At the time of its construction, the highway was the most northerly major road project to date. Weather and daylight conditions presented challenges. In 1979, a work crew was trapped in a blizzard in the Richardson Mountains and was almost lost. Construction had to account for the permafrost; heat transfer from the highway to the ground had to be prevented so the permafrost would not melt. To address this, the road was built on top of a gravel berm, ranging from 1.2 m (3 ft 11 in) up to 2.4 m (7 ft 10 in), to insulate the permafrost from the road above. Some construction was completed by the Canadian Forces; 3 Field Squadron, RCE from CFB Chilliwack built bridges over the Ogilvie River in 1971 and the Eagle River in 1977.