Positive Train Control A technology to keep us all safe

American rail systems are essentially safe. According to the Federal Railroad Administration, there has been a 14 percent decrease in the number of train accidents in the country between 2014 and November 2017.

Nevertheless, between collisions, derailments, human factors, and track, equipment, and signal causes, among others, we saw 1,492 train accidents in 2017 alone. Could we do better? How can we reduce the number of train accidents even further?

Positive Train Control (PTC)

A system that enhances train operation by combining locomotive, wayside, and signaling via wireless communication to reduce the possibility of:

  • train-to-train collisions
  • overspeed derailments
  • unauthorized incursions into established work zone limits
  • movement of a train through a track switch in the wrong position

The main goal of any train protection system is to stop a running train. A PTC restricts the train movement to an explicit allowance, and movement is halted upon invalidation.

PTC works through a network between three devices: a train's on-board computer, trackside 'ping' points, and dispatch stations. PTC systems may slow and/or stop trains that are cruising over posted speed limits.

The train's on-board computer receives information about its location and route–posted speed limits, known construction or hazards, and where it is allowed to travel safely. Equipment on board the train then enforces this, preventing unsafe movement.

Antenna or GPS signaling devices enable communication between dispatchers and the train's computer.

On occasion, these devices are embedded in the tracks.

The ping points provide dispatchers and train conductors vital information about how fast the train is going, where it is, and whether it needs to slow down.

The information generated by ping points along the route, and transmitted to the train computer, can alert a conductor if the train is moving too fast.

In an emergency, the train computer can override the conductor and apply the brakes.

Positive Train Control could also be used to prevent collisions between trains (since the system would know where each train is), keep trains from rolling into work zones, and stop trains from cruising through track signals left in the wrong position.

Various other benefits are sometimes associated with PTC, such as increased fuel efficiency or locomotive diagnostics.

The 2008 legislation mandated that all Class 1 freight RR install PTC, and that PTC should be installed on all line segments with passenger service, including commuter railroads.

These changes in railway safety are imminent. Congress has established December 31, 2018, as the installation deadline, while December 31, 2020, is the deadline for implementation.

Implementing PTC technology requires knowledge of train speed and constant calculation of stopping distance. It also requires knowledge of track alignment, speed limitations, other train locations, and track conditions.

Combination of all of the above must be calculated constantly.

In addition, all of the supporting information and systems used for calculations must be compatible across/between many different private and public railroads.

By knowing how train control and signaling systems are designed and operated, railway engineers will be able to increase capacity, reliability, and safety.

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