Positive Train Control — Ready to Go?

Now, with the regulatory structure in place, FRA is supporting the development, testing and implementation of several PTC prototype systems for freight, passenger and mixed traffic lines in the Pacific Northwest, Michigan, Illinois, Alaska and on the eastern seaboard. The PTC system design concept for each of these prototype systems varies, depending on the actual operational needs of railroads and the level of sophistication of existing signaling systems. Some implementation efforts are intended to satisfy the core objectives of the PTC concept by serving as an “overlay,” while the others are approaching the level of “vital application.” The vital applications aim to replace existing signaling systems or methods of train operations and extend system functionality to include issuance of movement authority and the control of wayside equipment through digital radio communication.

The configuration of each PTC system employed also varies depending on which of the two major elements of the system — dispatch/control center or the train itself — is responsible for the major decisions regarding safe operations. Some of the prototype PTC systems are office-centric or dispatch-based systems, while the others are mobile-based or train-based systems. Each has advantages and disadvantages within the overall conceptual framework provided by the regulation.

Technical Readiness
It is not the case that PTC is readily available “off the shelf” merely because most of its electronic components already exist. Nevertheless, recent system development efforts have achieved notable successes, as well as highlighted additional areas that will require further work.

As previously noted, Amtrak has successfully implemented two architecturally distinct types of PTC systems: ACSES on the Northeast Corridor (NEC) and ITCS on trackage it owns in Michigan. In December 2006, FRA approved the Product Safety Plan (PSP) for the Electronic Train Management System (ETMS) Configuration I, which applies to non-signaled territory and single-track traffic control territory on the BNSF Railway. Although approval of the PSP indicates FRA’s confidence that ETMS is safe, deployment outside the initial test bed and equipping of additional locomotives will be needed to prove that the system’s availability and performance fully support the railroads’ operational requirements. Further, the technical framework that is required to fully support mixed passenger and freight operations needs continues to be refined. It has yet to be fully demonstrated that on lines with heavy freight traffic, the PTC systems used by major freight railroads can be successfully configured to support passenger operations.

The major remaining technical challenges associated with PTC technology implementation include achieving and documenting the proven or validated interoperability between different PTC designs chosen by railroads operating over each other’s territories (as they routinely do), the deployment of a uniform and compatible human/machine interface, and — most importantly — the effective use of radio frequency bandwidth allocated for railroad industry operations with communication protocols that fully support the reliable operation of PTC systems.

There are nine ongoing PTC projects in the United States that illustrate alternative approaches for resolving these technical challenges. The projects involve nine railroads (predominantly Class I) and are located in 16 states. The systems are operated or tested on about 2,600 track miles. These projects are at different stages of development and maturation.

The ACSES system implemented by Amtrak on the NEC is a transponder-based system that enforces civil and temporary speed restrictions and positive stops at absolute signals. It is integrated with the nine-aspect cab signaling system and automatic speed control, completing the package of all PTC functionalities. It supports safe passenger rail movements at speeds of up to 150 mph, and two freight railroads operate equipped locomotives over portions of the territory. The ITCS system, employed by Amtrak in Michigan, is a train-based PTC system that employs wireless grade crossing activation and enforcement of speed restrictions and work zone boundaries. ITCS is authorized to allow passenger trains to operate at speeds of up to 95 mph on a mixed light-density freight/passenger corridor. Amtrak is currently conducting a verification and validation of the ITCS system to increase maximum allowable speed to 110 mph. Both of these Amtrak systems were grandfathered under the PTC rule, thus relieving the need to comply with its provisions.