Distributed power

Wired systems now provided by various suppliers use the cabling already extant throughout a train equipped with electronically controlled pneumatic brakes (ECP).

Since the 1960s, railroad distributed power technology has been dominated by one company, Harris Controls (originally Harris Corporation — Controls & Composition Division, later purchased by General Electric—the division now known as GE Transportation) who have manufactured and marketed a patented radio-control system with the trade-name of Locotrol, which is the predominant wireless DP system in use around the world today.

With its origins in the early days of SCADA technology for the remote control of pipelines and electric utilities, and from an early concept of Southern Railway President D.W. Brosnan, Locotrol was a product of the North Electric Company (Galion, Ohio) which was later purchased by Radiation Inc. (Melbourne, Florida) and—in turn—purchased by Harris Corporation (also headquartered in Melbourne).

In the early years of this technology, WABCO also had—for a relatively brief period—a competing system called "RMU" (Remote Multiple Uniter), which was installed on a few North American railroads.

Over an undulating track profile, a skillful operator can manipulate the relative power outputs (as well as dynamic- and air-brake applications) to minimize run-in and run-out of coupler slack throughout the train.

The main disadvantage is the operational time needed, and track configuration required, to add and remove additional locomotive units.

Secondary disadvantages are the costs associated with equipping locomotives with the extra control apparatus and the potential for the intermittent loss of the telemetry signal.

Originally the loss of connection would result in the remote units remaining in their last-commanded throttle or dynamic braking position.

Later system versions and software updates typically reduce the remote unit power setting to Notch 4 by default if the link is lost.

Distributed power in a wired configuration (using the ECP trainline) is becoming increasingly common in North American and Australian heavy-haul unit-train operations.

One use of a distributed power top-and-tail configuration is in Western Australia's wheatbelt, in which Locotrol provides an operational solution rather than increasing the train size.