The line included a 23-mile stretch over the top of the Continental Divide, at Rollins Pass, with a two to four percent grade and switchbacks along many sections; the result was one of the highest adhesion (non-cog) standard-gauge railroads ever constructed in North America.: This corridor over Rollins Pass was always intended to be temporary until what would later become the Moffat Tunnel was constructed and opened; therefore this overmountain route was constructed with more cost-effective materials: using wooden trestles (made of all Oregon fir) instead of iron bridges or high fills and wyes instead of turntables. Construction of this route was exceptionally dangerous and deadly: in a single day, 60 Swedish workers were killed when a powder charge exploded prematurely during the construction of Needle's Eye Tunnel.