Positive Train Control explained: How the safety system can prevent disaster

The deadly NJ Transit crash in Hoboken, New Jersey, has sparked a renewed discussion about Positive Train Control, a safety system that can prevent certain types of train crashes.

Following the 2013 Metro-North derailment that killed four people in the Spuyten Duyvil neighborhood of the Bronx, the National Transportation Safety Board concluded that the installation of PTC along the train route could have prevented the crash.

Although the NTSB has said investigators do not yet know the cause of the Hoboken crash or if PTC could have prevented it, we took a look at what the technology is and where the various transit agencies stand with installing it.

What is Positive Train Control?

Positive Train Control is a processor-based safety system that is designed to prevent train crashes and derailments. Should the operator of a train fail to take appropriate actions in certain situations (not stopping for a stop signal, for example), PTC is able to automatically take control of the train’s speed and movement to prevent error, according to the Federal Railroad Administration.

There are five types of PTC systems: ACSES (Advanced Civil Speed Enforcement System), ETMS (Electronic Train Management System), I-ETMS (formerly called Vital Electronic Train Management System), ITCS (Incremental Train Control System) and E-ATC (Enhanced Automatic Train Control).

How does PTC work?

The Association of American Railroads, an industry trade group that represents many major freight railroads and North America Amtrak, outlines three main elements to a PTC system.

First there is the locomotive system (also called onboard system), which tracks the train’s speed and location and can brake when necessary to keep within the speed limit. Second is the wayside system, which monitors track signals, switches and circuits, and relays to the train when it is authorized to move. The third component is the back office server, which stores all of the information about the rail network and the trains that use it, including speed limits, and tells a train when it is authorized to move into new segments of track.

The FRA said PTC systems vary widely in terms of equipment and how they operate. “Even the design of each system tends to be unique,” the FRA explains on its website.

For example, some systems use GPS and onboard devices to track trains, while other systems use track transponders.

What types of accidents can PTC prevent?

Most PTC systems can prevent train-to-train collisions as well as derailments that happen due to exceeding the speed limit. PTC also keeps trains from going into pre-established work zones and can stop a train moving through a main line switch in the wrong position, according to the FRA.

Are there types of accidents where PTC would be ineffective?

The Association of American Railroads says there are certain types of crashes that PTC wouldn’t be able to prevent, including track equipment failure, collision with a vehicle at a grade crossing, collision with a person trespassing on railroad tracks and “some types of train operator error.”

Is PTC mandatory on all railroad tracks?

There are some exceptions to the law, but for the most part, PTC is required to be installed and used on Class I railroad lines over which hazardous materials travel or passengers are transported, according to the FRA. The agency estimates the requirement covers about 70,000 miles of track across the country.

When is PTC supposed to be implemented?

In 2008, Congress passed a law requiring PTC to be installed on Class I rail lines by Dec. 31, 2015. You may have noticed, however, that even today not all train lines have PTC installed. That’s because in late 2015, Congress extended the deadline to Dec. 31, 2018. The new legislation, called the PTC Enforcement and Implementation Act, also allows for another two-year extension if certain requirements are met, according to the FRA.

Has PTC been installed on NYC area transit systems?

In May 2015, the FRA approved a $967.1 million loan to the MTA in order to help speed up installation of PTC on Metro-North Railroad and Long Island Rail Road tracks. The MTA said it is tasked with installing onboard components for 1,455 rail cars and transponders along 588 miles of track. A spokesman for the MTA said as of October 2016, PTC is on track to be rolled out across LIRR and Metro-North by the 2018 deadline. Currently, the system is not operational, however, the spokesman said the MTA is making progress toward a full systemwide implementation in two years.

Over at the Port Authority of New York and New Jersey, which operates the PATH system, crews are currently in the process of installing PTC on the Hoboken-33rd Street and Journal Square-33rd Street lines as part of its 10-year capital improvement plan. The Port Authority said it is currently on schedule to meet the 2018 deadline for PTC installation, due in part to its decision to suspend weekend service on those two lines in order to expedite the process.

According to NJ Transit’s annual report in 2015, the agency had began testing PTC on a single locomotive and cab car. Installation of PTC hardware along NJ Transit’s tracks was to begin in 2016, followed by full system testing. NJ Transit has not yet returned amNewYork’s call for comment on its current progress with PTC installation.