Union Pacific’s efforts to conduct a pilot program testing a one-person train crew configuration is facing an uncertain future.

UP (NYSE: UNP) wants to test out a train crew arrangement in which an engineer is in charge of moving a train while a grounds-based conductor — which UP calls “expeditors” — would respond to potential problems encountered by the train by driving a vehicle to the problem site.

The current arrangement calls for both a train engineer and conductor to be on a Class I freight rail train.

But union members with the transportation division of the International Association of Sheet Metal, Air, Rail and Transportation Workers (SMART-TD) have concerns about the program and the proposed configuration overall. They say such a program can’t — and shouldn’t — proceed without negotiations between union representatives and UP.

“There is NO agreement in place on any territory under our jurisdiction on Union Pacific property to run such [a] pilot program. The undersigned are duly recognized under the Railway Labor Act to be party to such agreement and take exception to Union Pacific’s false and misleading statement,” said a Jan. 13 letter from five general chairpersons of SMART-TD representatives to Kansas Attorney General Kris Kobach.

UP’s pilot program would have called for a conductor to remain on a train, with another grounds-based conductor also involved in the train’s operations as a way to compare both operational modes. If the pilot program went well, the railroad would implement this arrangement in controlled phases of increasing complexity, UP said during a December public hearing at the Federal Railroad Administration (FRA).

The railroads have also said that a train crew consisting of one person on the ground and another person in a locomotive cab would enable the industry to attract potential workers and retain existing ones who would otherwise be turned off by the long hours and unpredictable schedules.

In response to the union’s comments, UP said it remains in mediation with two SMART-TD committees over the proposed pilot.

“We cannot move forward without it being agreed upon through collective bargaining,” UP said in a statement to FreightWaves. “The proposed pilot enhances quality of life by placing the expeditor in a truck and dispatching them from a centralized home base to planned or unplanned events. They will be less likely to suffer the effects of fatigue” and face an unknown schedule.

The debate over train crew sizes comes amid FRA’s proposed rulemaking that would require freight trains to have at least two crew members in the locomotive cab. The rulemaking process has garnered hundreds of responses from both sides.

The railroads say positive train control (PTC), a safety technology that the Class I railroads spent millions to install in response to a federal mandate calling for the technology, performs some of the functions that a conductor handles now. Conductors traditionally have served as lookouts and advisers to train engineers, copying and acquiring directions from the dispatcher and communicating with the roadway worker in charge before entering a worksite. But in a territory where PTC has been implemented, it may no longer be necessary for the conductor to do these duties while inside the cab because the PTC system communicates this information directly to the engineer.

Short-line railroads also argue that the proposed rule includes them but shouldn’t since some short lines are smaller operations financially and in terms of the area they cover. Some have already been deploying one-person crews successfully.

But union members say trains need at least two people in the locomotive cab because it ensures safer operations. There are many unplanned situations in which a conductor can respond to an incident in a way that an engineer cannot, such as crossing gate failures or locomotive failures that may require switching locomotives within a locomotive consist. The absence of a conductor inside the cab could also overburden the engineer, who would need to keep track of the network updates provided by PTC in addition to performing regular functions.

Some union members also say the deployment of a one-person crew is an effort to cut costs in the name of precision scheduled railroading, a method adopted by the Class I railroads to streamline operations and reduce costs.

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