VIDEO: How Positive Train Control Works

December 19, 2017
Positive train control system combines GPS, wireless radio and computers

Monday's train derailment in Washington is bringing 'positive train control' (PTC) into conversations this week, so here is a brief PTC overview.

A positive train control system combines GPS, wireless radio and computers in order to monitor trains, and when necessary, stop them from colliding, derailing or speeding.

"We consider it an angel on our shoulders out there on the track, and it's our backup and our safety net," John Hyatt, a former railroad engineer, told CNN.

PTC was designed to prevent the human errors behind roughly 40 percent of train accidents by ensuring that it's being operated in accordance with signals, speed limits or other rules, rail safety experts say. It's an integrated system using tracks and train.

For example, if a train engineer doesn't see a curve coming or a spot where the train is supposed to slow down, signals are sent to the train and it will begin applying the brakes on the train to get it down to that speed which is required, or stopping the train.

"We have recommended PTC for decades," said National Transportation Safety Board member T. Bella Dinh-Zarr on Tuesday.

In 2008, Congress passed the Rail Safety Improvement Act of 2008 requiring the country's railroad companies to have PTC installed by December 2015. However, in late 2015 several railroad companies threatened to shut down services unless Congress gave them more time, maintaining the deadline wasn't realistic given the complex technology that requires the technology be installed on both locomotives and tracks. Congress extended the deadline to the end of 2018, with a possible extension to 2020 if certain Federal Railroad Administration requirements are met.

But it is slow going and costly. This is what railroad companies need to do by 2018:

  • A complete physical survey and highly precise geo-mapping of the more than 60,000 route -miles on which PTC technology will be installed, including geo-mapping of more than 486,000 field assets (mileposts, curves, grade crossings, switches, signals, and much more) along that right-of-way.
  • Install PTC technology onapproximately18,500 locomotives.
  • Install  approximately 29,500 “wayside interface units” (WIU) that provide the mechanism for transmitting information from signal and switch locations along the right-of-way to locomotives and railroad  facilities
  • Install  PTC technology on 1,900 switches in non-signaled territory and completing signal replacement projects at 14,500 locations.
  • Develop, produce, and deploy a new radio system specifically designed for the massive data transmission requirements of PTC at approximately 4,000 base stations, some 32,600 trackside locations, and on some 18,500 locomotives.
  • Develop back office systems and upgrade dispatching software to incorporate the data and precision required for PTC systems.

To make this national project even more difficult, since one railroad's locomotives may occasionally operate on another railroad's tracks, the PTC systems of both must be configured to recognize and respond to commands from a 'host' PTC system. Each railroad's PTC safety plan must be approved and certified by the Federal Railroad Administration before it can be activated.

Freight railroads have been working tirelessly to meet the PTC mandate. To date, they’ve spent more than $8 billion (their own funds, not taxpayer funds) on PTC development and deployment. The estimated total cost to freight railroads for PTC development and deployment is$10.6 billion, with hundreds of millions of additional dollars needed each year after that to maintain the system. The cost of PTC installation for U.S. passenger railroads is estimated at an additional $3.5 billion.

An example of PTC use is in Illinois, where a stretch of railroad that will run between Chicago and St.Louis at speeds of up to 110 mph is wrapping up after seven years and $2 billion of work.

Illinois Department of Transportation Secretary Randy Blankenhorn said in an interview with The State Journal-Register that the  St. Louis and Chicago high-speed line should be operational in 2019, pending installation of automated train-control and detection technology required for faster trains.

The current Amtrak speed limit between St. Louis and Chicago is 79 mph with the exception of a section of the line between Pontiac and Dwight, where demonstration speeds up to 110 mph started in the fall of 2012. At 90 mph, the current 5 1/2-hour trip between St. Louis and Chicago will be cut by 11 minutes and by 20 minutes when a second set of tracks is added in the Joliet area. Trains at 110 mph should save passengers 53 minutes.

In a heavily congested rail area like Chicago where high-speed rail is used by freight and passenger trains, PTC will address both safety and on-time performance.

“There’s architecture that needs to be developed. We’re running passenger trains with freight trains on a 110 mph corridor,” said John Oimoen, chief of IDOT’s rail division. “The infrastructure on the ground will be complete next spring. It’s the challenge of developing the software and getting that information back to (train) dispatch.”