The man who brought fail-safe brakes to railroads once had a major role in the 20th-century industry, but a combination of events and decisions have left only his braking system as a recognized legacy.
Thus far, we have looked at the classic, and still widely used fail-safe pneumatic brake (Part 1 and Part 2) However, a pneumatic-only system seems like an outdated antique in our electrical, electronic, and software-driven “smart” world. In fact, modern diesel locomotives have highly advanced power semiconductors and traction motives supported by software, providing advanced motor control, optimization of many functions, and energy efficiency, so why not use electrical activation for the brakes?
While the venerable air brake developed by George Westinghouse and greatly improved in over one hundred years of in-field use is effective and reliable, it has weaknesses that have also been recognized since the earliest days. These have become more serious as freight trains have gotten longer, heavier, and faster, often carrying hazardous cargoes.
The biggest drawback is the lag along the train once the brakes are applied. It can take one to two minutes for the brake signal and application to reach the back of a 50 to 100-car train. (Always keep in mind that a train is like a chain of semi-independent links, and while they are coupled, the coupling links are not rigid, and there is lots of flex.) This propagation delay means that the braking of cars will happen at different times along the train; in fact, while some cars are slowing down, others are still trying to push, unbraked, from the rear. The reverse is also true: when releasing the brakes, the front of the train may be pulling the rear cars, which are still braking. This is quite different than the direct cause/effect the driver controls when braking or accelerating in a car.
An alternative braking-system design which has been used in limited circumstances is electro-pneumatic (E-P) braking, which retains the power and mechanism of the pneumatic brake-shoe arrangement but under electrical control. In E-P braking (Figure 1), an electrical-control wire “instantaneously” transmits a control signal via an electrically operated pneumatic valve in each car. This is conceptually simple, but there are many subtle electrical and pneumatic issues to consider as well as basic reliability, back-up, and fail-safe considerations (References 7 and 8).
Versions of E-P braking were first introduced in the early years of the 20th century for subways or metros. The growth of rapid transit systems in cities with their large number of frequent stops and starts meant that quick responses to brake commands and accurate stopping at stations was a priority. They were tried on the New York Subway in 1909 and then on London Underground in 1916. and E-P braking is now used on main-line passenger railways as well as on specialized, dedicated-line freight operations such as those between an ore mine and its matching mill.
E-P braking offers speed of control and reaction times, resulting in instantaneous control of the whole train to the driver’s directives and the ability to better “modulate” the braking action. It also is a good fit for computer-based automatic train operation (ATO). It overcomes some issues with air-pressure drawdown and recharging of air pressure in each car’s air-reservoir tank.
E-P braking is not the same as electronically controlled pneumatic (ECP) braking (again, Reference 7). ECP brakes are ”smart” brakes with many additional benefits and features, somewhat similar to what modern automobiles have. Among these are anti-skid control, adaptive control based on load and speed, and related features. The associated electronics need battery power, of course, which can come from a DC supply line, a battery onboard each freight car. They can even be recharged by the moving freight car via an onboard generator. This is all simple in concept but challenging in execution in the real world of railroading.
Note that E-P and ECP brakes are not the same as dynamic brakes or regenerative brakes. In dynamic braking, the traction motors which drive the wheels of the diesel locomotive are switched to function as generators during the braking phase and dissipate this energy as heat in top-mounted air-cooled resistors. This reduces wear on the locomotive brakes, but can only be used with locomotives, as the cars and wheels of a standard freight train are unpowered (passenger coaches may be self-powered on commuter, and subway and specialty dedicated systems). In contrast to dynamic brakes, regenerative brakes take this motor-generator process one step further and feed the power produced by the motor-generator back onto the grid. This capability applies, of course, only to locomotives which run on catenary wires. Note that automotive hybrid and all-electric vehicles (HEV/EV) send regenerative power to an onboard battery to improve gas mileage or range. Still, batteries for storing the power are massive – although some energy-efficient locomotives do have onboard energy capture batteries.
What’s the status of E-P brakes for railroad freight cars? In a word, it’s “on hold” for many reasons. Depending on who you ask, the models, simulations, and road tests show that they can significantly improve train control, reduce stopping distance and accidents, and reduce accident severity – or have little if any benefit (References 9 and 10). Also, there are major cost and compatibility issues. Unlike dedicated commuter trains and simar constrained trainsets, railroad freight cars are randomly switched and coupled as complete trains are made up and broken apart in switchyards. This means that ensuring an entire train has freight cars equipped with E-P brakes plus a suitable locomotive (whether new or upgrades) is a logistical nightmare, as there are about 1½ million freight cars in North America and approximately 35,000 locomotives (not all are in “public use”; some are used on restricted, pre-assembled “single-unit” trains (Reference 11).
Part 4 will look at the many changes and near-disappearance of the Westinghouse Engineering Company, and lessons for the present.
EE World References
RCA
RCA & Color TV: A dominant company and standard, both now gone – Part 1Z
RCA & Color TV: A dominant company and standard, both now gone – Part 2
Locomotives
Electrified Locomotives, Tunnels, and the Pennsylvania Railroad: Astonishing engineering but a partially sad ending, Part 1: The challenge
Electrified Locomotives, Tunnels, and the Pennsylvania Railroad, Part 2: The tunnels
Electrified Locomotives, Tunnels, and the Pennsylvania Railroad, Part 3: The station
Catenary power
Electric locomotives and catenary power systems – Part 1: basic functions
Electric locomotives and catenary power systems – Part 2: power needs
Electric locomotives and catenary power systems – Part 3: power delivery
Electric locomotives and catenary power systems – Part 4: maintenance and corona
External References
- S. Patent 144006, “Improvement in steam and air brakes”
- The Traffic Accident Reconstruction Origin (TARO), “An Introduction to Train Brakes”
- Funding Universe, “Westinghouse Electric Corporation History”
- The Economist, “Westinghouse RIP”
- Engineering and Technology History Wiki, “Westinghouse Electric Corporation”
- Garbedian, H. Gordon, “George Westinghouse: Fabulous Inventor,” Dodd, Mead, 1943.
- The Railway Technical Website, “Electro-Pneumatic Brakes”
- net, “Braking Systems”
- Trains, “Electronically controlled pneumatic brakes study ‘inconclusive’ ”
- Trains, “The war over electric brakes”
- Statistica, “North American freight rail cars in service from 2009 to 2019, by car type”
