The long and the short of distributed power

Canadian Pacific has harnessed the latest train control and planning technologies to drive forward its successful long-train program.

With locomotives and cars lying idle, and uncertainty about the recovery, CP seized the opportunity to find innovative ways of improving productivity.

“We had to figure out how to leverage the bad news of deep recession,” explains CPR President and CEO Fred Green. “We’ve always had aspirations to run longer trains using distributed power, but when the railway is busy, testing can cause collateral damage to normal traffic. This was an ideal opportunity to validate the modeling we had already done on DP.”

The drive to extend train lengths has traditionally been constrained by issues such as excessive in-train slack action, deterioration of air brake signal propagation, and stress on infrastructure and equipment. Overcoming these difficulties with the aid of DP offers rich rewards. In addition to the obvious benefits of increased payload, DP reduces lateral forces and friction, lowers the impact of heavy trains on track, provides better adhesion and fuel economy, and can assist operations in low temperatures. Furthermore, CP estimates that labor costs on a typical transcontinental train are 30% lower than they would be if the railroad had stuck with shorter trains.

In its most basic form, DP has been used on CP’s British Columbia coal operations since the 1960s. But recent technological advances, including the development of advanced train modeling software and sophisticated onboard radio communications systems, have made DP suitable for a much broader range of operations, including intermodal and mixed trains. CP’s longest trains now reach 14,000 feet and the company is confident it can safely go even further in the future as it gains experience and the technology matures.

The core onboard technology is GE’s Locotrol system, which provides synchronous or independent control of locomotives, distributed in up to four locations along the train, which follow power and braking commands from the lead locomotive. The head end controlling locomotive controls the DP units or “remotes” along the train by sending command signals transmitted over radio links. Locotrol is designed to allow several trains to operate on the same radio frequency and within range of each other without interference.

Locotrol uses radio as a telemetry link to provide the precise timing required for coordinated communication between the lead and remote locomotives. This has three key advantages:

• Adhesion forces are distributed through the train, reducing drawbar and lateral forces and effectively transforming the train into smaller sectioned trains, enhancing tonnage capabilities.

• Brake application and release commands are transmitted by the same radio communication protocol, significantly shortening all brake command propagation times.

• Stopping distances are reduced through faster brake application, and more rapid acceleration and deceleration is possible.

Control functions are transmitted by the lead locomotive in a specific message format and protocol. The remote locomotives can then determine what function is actuated and perform that function in unison with the lead locomotive. The lead locomotive transmits a message a minimum of once every 20 seconds, when the engineer changes a command, or when the remote does not respond to the commanded message. Remotes are immediately notified of a control change by the lead and notify the lead that the command has taken place.

These communications occur in less than one second, and Locotrol periodically performs communications checks on both the lead and remote units to ensure consistent connectivity. When the check is unsuccessful, the backup radios intervene. If this fails, a communication interruption is declared. If continuous communication is not restored, a penalty brake application is automatically propagated throughout the train.

The possibility of wayside interference frequencies, operation in tunnels, or momentary malfunction of radios means there could be occasional instances where communication between the lead and the remotes is lost. If communication is lost for more than 45 seconds, a communication interruption condition is signaled, whereby the head end unit displays show the last status of the remotes. During this time the lead cannot communicate commands to the remotes, which continue to operate the last function commanded prior to the communication loss.

When there is a loss of radio communication, a significant propagation of the brakes is one method of isolating the remotes. When this occurs, the remotes cut out their feed valve and begin what is known in Locotrol as the Communication Loss Idle Down (CLID) procedure. This means that when the remotes sense a brake pipe reduction while in a state of communication loss, they automatically step down traction and cut out the brake valve. If in Dynamic Braking (DB), the DB force will me maintained.

When communication is re-established, the operator in the lead unit follows a special sequence of key functions to cut the feed valves back in and recharge the train from the head end. Each remote needs to sense a rise of 4 psi per minute in its brake pipe to automatically cut in the feed valve.

In cooperation with GE Transportation, Wabtec, and New York Air Brake, CP has carried out a series of field tests on CLID performance, monitoring the impact of parameters such as air flow and brake pipe leakage on propagation. These tests involved three different types of train (coal, intermodal, and autorack) looking at different flow rate conditions and train section lengths. The study found that CLID can propagate successfully and safely at levels well beyond the current maximum total train air flow of 60 cubic feet per minute and possibly as high as 90 cfm. It also validated the concept of operating with multiple remotes, making a long train resemble a series of short trains, synchronously connected to the lead.

At present, train length in Canada is governed entirely by the railroads themselves, although Transport Canada has kept a close watch on developments following a series of derailments involving CN trains. Like CP, CN has been gradually building up train lengths in recent years, and originally favored increasing head end power over DP. However, since the derailment of an 8,850-foot-long train at Brighton, Ontario, in March 2009, which was found to be the result of excessive in-train forces, CN has limited conventionally hauled trains to 8,500 feet and is now actively expanding use of DP.

In February, Transport Canada launched a two-year study into long trains, with the aim of developing scientifically-informed regulation of their operations. The country’s Transportation Safety Board notes that DP significantly improves control of in-train forces through better air brake response and during service release and recharge, but it also warns that the placement of DP within the train and the length/tonnage behind or ahead of each placement point must be pre-established.

CP is the safest railroad in North America for train incidents, and the company is keen to ensure its record is not compromised by the introduction of longer trains. Like DP, recent developments in train planning software have been invaluable to the safe implementation of the long train program. CP uses Train Area Marshalling (TrAM) software to assemble trains, which guides front-line employees on locomotive and car placement and to manage in-train forces and determine the optimal position of the locomotive within a consist, taking account of the topographical features the train will encounter on its journey. Together, TrAM and DP have reduced derailments by 50%.

CP is now investing in its track to support the wider deployment of longer trains. “Having validated the concept, we have to go back and complete the buildout of the necessary infrastructure,” says Fred Green. “Every siding constructed in the past five years has been built to accommodate longer trains, including those on our main route to Chicago. Within three years we will have the entire infrastructure in place to run as many of these trains as we aspire to.”

(This article is based on “Long Train Testing and Validation at Canadian Pacific,” a paper by A. Aronian, K. Wacks, S. Bell of Canadian Pacific; and D. Peltz of GE Transportation, presented at the International Heavy Haul Conference, Calgary, June 22, 2011.)