Question: Highway 42 runs northwest from where Highway 24 crosses the BNSF Railway's Northern Transcon,  a route operated by what Railway?

Context paragraphs:
Morris Subdivision: The Morris Subdivision or Morris Sub is a railroad line that runs about 113 mi from Breckenridge to Willmar, Minnesota.  Currently operated by BNSF Railway, this was part of the Great Northern Railway's transcontinental line from Minneapolis to Seattle, Washington.  Today (as of 2010), BNSF's Northern Transcon travels up the Staples Subdivision instead, which is a more direct route to Fargo, North Dakota.

Wayzata Subdivision: The Wayzata Subdivision or Wayzata Sub is a railway line that runs about 93 mi from Willmar to Minneapolis, Minnesota.  Currently operated by BNSF Railway, this was part of the Great Northern Railway's transcontinental line from Minneapolis to Seattle, Washington.  Today, BNSF's Northern Transcon travels up the Staples Subdivision instead, which is a more direct route to Fargo, North Dakota.  As of May, 2011, the route is of moderate capacity and typically sees around 15 trains per day.

Scenic Subdivision: The Scenic Subdivision or Scenic Sub is a railway line running about 155 miles (249 km) from Seattle, Washington to Wenatchee, Washington.  It is operated by BNSF Railway as part of their Northern Transcon and contains the Cascade Tunnel as well as the final spike completion site, in 1893, at Scenic Hot Springs, for the whole Great Northern Railway transcontinental railway line built by James J. Hill.

St. Paul Subdivision: The St. Paul Subdivision or St. Paul Sub is an 30.9 mi railway line running from Minneapolis through neighboring Saint Paul, Minnesota and on into Saint Paul's southeastern suburbs along the Mississippi River.  It is a segment of BNSF Railway's Northern Transcon which runs from Chicago, Illinois to Seattle, Washington.  Between Minneapolis and Saint Paul themselves, this route runs on former Northern Pacific Railway trackage, and now forms the northern set of BNSF tracks running between the two cities.  The companion route running slightly to the south is the Midway Subdivision, though the St. Paul Subdivision is the busier set of tracks, hosting about 59 trains per day as of April 2009.  It is the second-busiest rail line in the state, after the segment of the Staples Subdivision between Fridley and Coon Rapids.

Aurora Subdivision: The Aurora Subdivision or Aurora Sub is a railway line in Wisconsin and Illinois operated by BNSF Railway.  It is part of BNSF's Chicago, Illinois, to Seattle, Washington, Northern Transcon.  This segment runs about 262 mi from the St. Croix Subdivision in La Crosse, Wisconsin, to the Chicago Subdivision in Aurora, Illinois.

Montana Highway 42: Montana Highway 42 (MT 42) is a short, 2.9 mi state highway in the U.S. state of Montana, connecting Montana Highway 24 with downtown Glasgow.  Formerly Highway 24W, Highway 42 (its route number a reversal of "24") runs northwest from where Highway 24 crosses the BNSF Railway's Northern Transcon, staying parallel to the tracks until it turns right in Glasgow's downtown and dives under the railroad to meet with and terminate at U.S. Route 2.

Columbia River Subdivision: The Columbia River Subdivision or Columbia River Sub is a railway line running about 167 mi from Wenatchee to Spokane, Washington.  It is operated by BNSF Railway as part of their Northern Transcon.  The original line (built in 1893) was built as part of James J. Hill's Great Northern Railway transcontinental railway line.

Chicago Subdivision: The Chicago Subdivision or Chicago Sub is a railroad line in Illinois that runs about 38 mi from Chicago to Aurora and hosts Metra's BNSF Railway Line commuter service.  It is operated by BNSF Railway as the easternmost part of the railroad's Northern Transcon to Seattle, Washington.  This line is known as the Racetrack because it is mostly triple-tracked and supports fairly fast trains.  It had been operated by a BNSF ancestor, the Chicago, Burlington and Quincy Railroad, which introduced high-speed "Zephyr" passenger trains in 1934 and ran many of them along this subdivision from Chicago to points west.

Northern Transcon: The Northern Transcon, a route operated by the BNSF Railway, traverses the most northerly route of any railroad in the western United States.  This route was originally part of the Chicago, Burlington and Quincy Railroad, Northern Pacific Railway, Great Northern Railway and Spokane, Portland and Seattle Railway systems, merged into the Burlington Northern Railroad system in 1970.

Midway Subdivision: The Midway Subdivision or Midway Sub is a 12.4 mi railway line in Minneapolis and Saint Paul, Minnesota on the BNSF Railway's Northern Transcon which runs from Chicago, Illinois to Seattle, Washington and Portland, Oregon.  This is former Great Northern Railway trackage, and now forms the southern set of BNSF tracks running between the two cities.  The companion route running slightly to the north is the St. Paul Subdivision, former Northern Pacific Railway tracks.  The Midway Subdivision hosted about 24 trains per day as of September 2015.

Supporting paragraphs: Montana Highway 42 Northern Transcon
Answer: BNSF