Positive train control

Positive train control (PTC) is a family of automatic train protection systems deployed in the United States. Most of the United States' national rail network mileage has a form of PTC. These systems are generally designed to check that trains are moving safely and to stop them when they are not. A simplistic form of train traffic governance is negative train control, where trains must stop when issued a stop order and can move in the absence of such. An example of negative train control is Indusi. In contrast, positive train control restricts the train movement to an explicit allowance; movement is halted upon invalidation. A train operating under PTC receives a movement authority containing information about its location and where it is allowed to safely travel. PTC was installed and operational on 100% of the statutory-required trackage by December 29, 2020. The American Railway Engineering and Maintenance-of-Way Association (AREMA) describes positive train control systems as having these primary functions: Train separation or collision avoidance Line speed enforcement Temporary speed restriction enforcement Rail worker wayside safety Blind spot monitoring. In the late 1980s, interest in train protection solutions heightened after a period of stagnant investment and decline following World War II. Starting in 1990, the United States National Transportation Safety Board (NTSB) counted PTC (then known as positive train separation) among its "Most Wanted List of Transportation Safety Improvements." At the time, the vast majority of rail lines in US relied upon crew members to comply with all safety rules, and a significant fraction of accidents were attributable to human error, as evidenced in several years of official reports from the Federal Railroad Administration (FRA). In September 2008, Congress considered a new law that set a deadline of 15 December 2015 for implementation of PTC technology across most of the US rail network.