An engineering marvel for its time, the Loop was constructed to overcome the steep grade between Grandview at mile 44 and the tunnel at mile 51. The four-story loop circled back on itself on high trestles to avoid the side hill tracks and tunnels required of a more traditional route. Costly to maintain, the Loop was bypassed with a new route in 1951. By that time, more powerful diesel engines had replaced steam engines and were better able to manage the steep grade.
The Loop was dismantled, causing the Alaska Railroad Track to shorten by a mile. The mileposts along the track now read, 49…51.