Automatic Train Stop (ATS) systems have been used throughout the world on many different types of railway operations. ATS provides an additional layer of safety by helping prevent trains from passing stop signals and exceeding speed restrictions at critical locations.
ATS has historically been used on main line railways carrying both passenger and freight traffic. These systems provide protection against Signal Passed At Danger (SPAD) incidents and help improve overall railway safety.
Many commuter rail systems adopted ATS because of the high frequency of train operations and the need to provide additional protection in areas with frequent stops and dense traffic.
Older commuter rail networks often installed ATS as a practical and cost-effective method of improving safety before more advanced train control technologies became available.
Urban transit systems, including subway, metro, and light rail systems, have also used ATS. In many cases, ATS was employed to prevent trains from entering stations at excessive speed or operating unsafely through sharp curves and restricted areas.
Freight railroads have used ATS on selected routes, particularly where freight and passenger trains share track or where specific safety concerns have been identified.
ATS may also be installed at locations with elevated safety risks, such as steep grades, busy junctions, areas with limited visibility, or locations with a history of signal violations.
In some situations, ATS serves as an interim safety measure while a railroad plans, designs, or installs a more advanced train protection system such as Automatic Train Protection (ATP) or Positive Train Control (PTC).
Many railroads have gradually upgraded from ATS to more advanced systems. However, ATS continues to operate in some locations as a legacy safety system because it still provides valuable protection against critical operating errors.
Although ATS remains an important safety tool, it is generally considered less comprehensive than ATP because ATS typically provides protection only at specific locations rather than continuously supervising train movement.