Dark territory is a term used in the North American railroad industry to describe a section of running track not controlled by signals. Train movements in dark territory were previously handled by timetable and train order operation, but since the widespread adoption of two way radio communications these have been replaced by track warrants and direct traffic control, with train dispatchers managing train movements directly. Today most dark territory consists of lightly used secondary branch lines and industrial tracks with speeds ranging between 25 miles per hour (40 km/h) and 40 miles per hour (64 km/h), however there do exist a small minority of main lines that fall into the category. The term can also apply to automatic signaled lines where trains are running against the normal flow of traffic.
The primary safety concerns with dark territory stems from the lack of any form of direct or indirect train detection along the route. Train detection systems such as track circuits not only alert other trains to the presence of a potential hazard, but can also alert dispatchers or other monitoring systems to the same. Dark territory also lacks the ability to control or lock switches onto the main track, detect misaligned switches, broken rails or runaway rail cars. In most cases these drawbacks are mitigated by the light traffic and low speed of the trains in dark territory, but a runaway train (such as the crude oil unit train in 2013's Lac-Mégantic derailment) will not respect limits on speed and is not detectable by rail traffic controllers on a line with no signals or track circuits.
The total reliance on manual procedures to ensure safety has occasionally resulted in train wrecks, some with fatalities, due to either miscommunication or oversight on the part of operating personnel. In 1948 the Interstate Commerce Commission set a nationwide speed limit of 60 miles per hour (97 km/h) for trains not protected by some kind of block system (including manual block and track warrants) and in 2012 this was expanded to include all lines considered dark territory. Since 1991 the National Transportation Safety Board (NTSB) had recommended that railroads be required to install new forms of signaling technology, such as positive train control (PTC), that can stop trains from exceeding their procedural authorities and warn them of improperly lined switches. In 2008 Congress passed a law requiring installation of PTC technology on parts of the U.S. rail network, including some dark territory, by 2016, although as of 2012 none of the proposed implementations have been rolled out on a regular basis for freight trains.
On specific railroads
The Gateway Subdivision of BNSF Railway, in California and Oregon, is unsignalled and operates with track warrant control (TWC), as is the El Paso Subdivision located in Southern New Mexico. The Phoenix Subdivision is an approximately 200-mile-long mainline subdivision running north/south in Arizona operating under verbal track warrant. 
Iowa, Chicago and Eastern Railroad
Dakota, Minnesota and Eastern Railroad
The Waseca Subdivision of the Dakota, Minnesota and Eastern Railroad, a 103 mile (166 km) freight line in Minnesota, is not signalled and uses TWC. Several other portions of the railroad converted to signalled operation in 2008.
Long Island Rail Road
The Long Island Rail Road in New York, the nation's busiest commuter railroad, still operates two sections of track in dark territory. The Montauk Branch between Speonk station and Montauk, as well as the Main Line between Ronkonkoma and Greenport, operate without any signalling or Automatic Train Control system. Train crews must receive permission from the Block Operator to traverse those sections of the railroad in the form of train orders, in addition to strictly adhering to the rules and special instructions of the railroad's timetable.
Union Pacific Railroad
The Union Pacific Railroad uses dark territory on the Sharon Springs Subdivision in western Kansas, the Lost Springs Subdivision between Herington, Kansas and Wichita, Kansas, as well as on several under-used lines in the Greater Los Angeles Area.
- U.S. National Transportation Safety Board (NTSB)(2006). Washington, D.C. "Failure to Adhere to Track Warrant Control Rules Caused Collision of Two BNSF Trains in Gunter, Texas, NTSB Says." Press Release, June 13, 2006.
- Transportation Safety Board (Canada) investigation R13D0054, Lac-Mégantic derailment of 6 July 2013
- NTSB (1991). "Original 'Most Wanted' List of Transportation Safety Improvements, as adopted September 1990." Note: The original NTSB list used the term "Positive Train Separation," which was revised to "Positive Train Control Systems" in 1991.
- U.S. Rail Safety Improvement Act of 2008, Pub.L. 110–432, 122 Stat. 4848, 49 U.S.C. § 20101. Approved 2008-10-16.
- Elmquist, Sonja (2011-01-19). "GE-Tessco Train-Safety Gear to Cover "‘Dark Territory’". Bloomberg.com.
- U.S. Federal Railroad Administration (FRA), Washington, DC (2005). "Accident Investigation Report HQ-2005-03: Burlington Northern Santa Fe (BNSF), Bieber, California, January 8, 2005." Accessed 2011-04-29.
- Minnesota Department of Transportation, St. Paul, MN (2009)."Freight Rail Supply and Demand; Draft Technical Memorandum." Minnesota Comprehensive Statewide Freight and Passenger Rail Plan. p. 3-12.
- Stagl, Jeff (10 2008). "Suppliers tweak train-control systems to help railroads avoid dark territory accidents". Progressive Railroading (Milwaukee, WI: Trade Press Media Group).
- FRA (2005). "Railroad Switch Safety Demonstration Begins Testing." Press Release, November 14, 2005.