Montana Rail Link SD45 No. 377 pops out the the east portal of Mullan Tunnel west of Skyline, Montana, on September 3, 2003. The unique “squirrel cage” round duct structures on both side of the portal hold ventilation fans that are used to evacuate exhaust smoke and fumes from the bore. They were installed by Northern Pacific in 1948, with twin 250-horsepower fans blowing air out the west portal. The fans were deactivated by BN in the 1970s, but MRL reactivated the right one in 1993 to help with smoke issues. Both were removed in June 2009 as part of extensive Mullan Tunnel clearance improvements.
