The Northern Pacific Railway (NP) used the pass for its line from Logan to Garrison via Helena, built in 1883. This line was the NP's primary freight route and was also used by their secondary passenger train, the "Mainstreeter". The NP also built an alternate line over Homestake Pass, which was used by their primary passenger train, the "North Coast Limited". The rail line at Mullan Pass is currently operated by Montana Rail Link; it crosses under the pass and the continental divide at via the Mullan Tunnel.