The entire PTC concept is that there is a communications-based rail network in place. This means the train operator makes the decision about what the train is going to do, how fast it’s going to go and what it’s limits are but makes that decision based up on information that he receives from the onboard computers with database and location information along with what he receives from the wayside signaling system. The only way the operator can get that information is from the wayside or office via radio; a radio link must be in place to know what the signals are commanding or the operator must stop the train.

The radio system provides the ability to have virtual signaling and have the ability to control the train from different locations. It’s the essence of PTC to have a radio band that enables everybody to have the same frequency and is critical to the initiative’s success. The back office must be able to communicate to the base station via LAN line and then that base station transmits the data from the office to the locomotive. The wayside devices transmit their data to the locomotive too but that is a local communication. The key is to make sure that where there has to be wireless activity that there is a communications method between the wayside systems and the train and the base stations and the train.

Interoperability is key so that as trains crossover and responsibilities overlap from commuter trains to freight trains while sharing track, the various trains are controlled in the same manner. This eliminates much variance along the network.

Regarding radio communications, the Rail Safety Improvement Act does state that the railroads must have enough bandwidth to accommodate PTC, and that this radio system must include secure encryption and authentication.

The railroads have agreed to use a 220 megahertz (MHz) radio band for PTC. In the past, the railroads used 900 MHz for train control. Interoperable train control 220 will be the over the air protocol that allows everyone to talk on the same channel. The advantage of using a 220 MHz radio frequency is that it has excellent range. There will need to be a base station every 20 – 30 miles; a typical base station is a 100-foot tall tower that includes antennas and several radios with multi-channel receivers and can see up and down the length of the track. If there are several tracks in the area it can have a bank of radio channels that the trains can log onto and use as they’re traveling throughout the area. All of the wayside devices have an antennae with a much shorter length of frequency range and can either communicate directly to the train or through to the base station and then to the train. However, they only have a reach of about five miles.