PTC vs ITC vs CTC

Written by Robert Romaine

Here's a great point of clarification. ITC, ITCM, PTC and CTC are often conflated, which is understandable! This is my understanding of the differentiation, and I also welcome corrections or clarification.

ITC / ITCM

ITCM stands for Interoperable Train Control Messaging. This is essentially the messaging infrastructure that allows applications in the back office, locomotives, waysides and other parts of the system to communicate. It can use a variety of underlying transports, including 220 MHz radio, cellular, satellite and hardwired IP networks.

A major portion of the 220 MHz traffic is what we're receiving with ITCMon.

PTC

PTC is the safety overlay mandated by the Rail Safety Improvement Act of 2008. Its purpose is to prevent certain train to train collisions, overspeed derailments, incursions into work zones and movements through improperly positioned switches.

PTC uses the ITC communications system to exchange the information it needs. Of particular interest to us are the Wayside Status Messages broadcast by WIUs, which report the status of signals and switches. These broadcasts constitute the bread and butter of what we're listening to.

CTC

This is the system we all know and love. CTC is the railroad's traffic control system used by dispatchers to control signals and switches and receive indications from the field, including track occupancy.

Historically, much of that field to office communication was carried over protocols such as ATCS. Today it can be transported over a variety of communications systems, including fiber, cellular, satellite, and in some cases the ITC network.

So to answer your last question directly: yes. What we're primarily working with right now is the PTC wayside information broadcast for locomotives, particularly signal and switch status. Not the complete CTC information available to the dispatcher.

Hopefully that helps clear up some of the terminology. It's a lot of new information for a lot of us!