Rail systems

Rail systems in many parts of the world use the Global Positioning System (GPS) in combination with various sensors, computers, and communication systems to improve safety, security, and operational effectiveness. These technologies help to reduce accidents, delays, operating costs, and dangerous emissions, while increasing track capacity, customer satisfaction, and cost effectiveness. Integral to the efficient operation of rail systems is the requirement for accurate, real-time position information of locomotives, rail cars, maintenance-of-way vehicles, and wayside equipment.

Ensuring high levels of safety, improving the efficiency of rail operations, and expanding system capacity are all key objectives of today’s railroad industry. Unlike most other modes of transportation, there is little flexibility in managing rail traffic. Most rail systems are comprised of long stretches of a single set of tracks. Trains bound for thousands of destinations must simultaneously share the use of these single line tracks.

Precise knowledge of where a train is located is essential to prevent collisions, maintain smooth flow of traffic, and minimize costly delays due to waiting for clearance for track use. Only the skill of the crews, accurate timing, a dynamic dispatching capability, and a critical array of “meet and passes” locations on short stretches of parallel tracks, allow rail dispatchers to guide their trains safely through. It is therefore critical for safety and efficiency reasons to know the position and performance of these trains both individually and system-wide.

GPS also contributes to dependable scheduling through train location awareness, enhancing connectivity with other modes of transportation, such as rail station to airport transfers.

An enhancement to the basic GPS signal known as Differential GPS (DGPS) improves accuracy and safety within its coverage areas. The enhanced position information enables the dispatcher to determine on which of two parallel tracks a train is located. When coupled with other location and navigation devices to account for time in tunnels, behind hills, and other obstructions, DGPS can provide a reliable and accurate position-locating capability for rail traffic management systems.

Differential GPS is an essential element of the Positive Train Control (PTC) concept being adopted in many parts of the world. This concept involves providing precise railroad position information to sophisticated command and control systems to produce the best operating plan to include varying train speed, re-routing traffic, and safely moving maintenance crews onto and off tracks.

A PTC system can track the location and speed of a train more accurately than was previously possible, providing train movement information to rail management personnel who can then enforce speeds and limits of authority, as necessary. By providing better tracking of train location and speed, PTC increases operational efficiency, allows higher track capacity, enhances crew, passenger, and cargo safety, and also results in a safer environment for personnel working on the track.

Differential GPS can also aid in surveying and mapping track structure for maintenance and future system planning. By using DGPS, one can precisely locate mileposts, signal masts, switch points, bridges, road crossings, signal equipment, etc. GPS can satisfy the high level of accuracy needed for operation in terminal areas and rail yards, where dozens of tracks may run in parallel.

Finally, with the modernization of GPS, rail operators can look forward to providing better service. In addition to the current GPS civilian service, the United States is committed to implementing two additional civilian signals. Access to the new signals will mean increased accuracy, more availability, and better integrity for all users.