Early next year, some Metro employees will be asked to log their activities and wear motion-detecting devices that resemble wristwatches in an effort to measure how much they sleep — or don’t sleep — and the effect of sleep habits on their jobs.

The monitoring is part of Metro’s effort to combat fatigue among safety-critical employees, including those who operate and maintain buses and trains. Officials commissioned the study after an earlier one raised concerns about worker fatigue.

The earlier study, released in November 2011, found that Metro employees in safety-critical jobs worked longer hours than allowed and that there were no limits on the number of consecutive days worked. After receiving the results, Metro officials took steps to limit the number of hours some rail employees could work.

Steven R. Hursh, president of the Baltimore-based Institutes for Behavior Resources, the firm working with Metro on the study, told members of the Metro board’s Safety and Security Committee at a meeting Thursday that the number of hours an employee works is not the only factor that contributes to fatigue.

The problem, Hursh said, can be aggravated by a failure to get enough sleep and by an employee’s work schedule. Workers with late-night shifts are particularly vulnerable to fatigue because they are awake during hours when people typically get the best sleep, he said.

Although the solution may be as simple as more sleep, ensuring that employees get enough rest is more complicated, Hursh said.

Federal regulations limit the number of hours a rail engineer, truck driver or pilot can operate a railroad train, a truck or a plane, but there are no such rules for transit workers. At Metro, the maximum number of hours an employee can work is set by the collective-bargaining agreement with the union.

Hursh’s analysis of worker hours found only a small number of bus and rail operators worked hours that exceeded federal standards for action in other fields. Still, Metro officials remain concerned about the impact on those workers.

One solution might be to rotate shifts, allowing those who work the night shift to work an occasional day shift. But Hursh said he recognized that might not be possible for some jobs at Metro.

Metro officials are asking for $5.5 million in fiscal 2014 to fund a second phase of fatigue-management efforts. Richard Sarles, the agency’s general manager, called the study a “major step.”

Board members also were briefed on new plans for Silver Line service .

During a series of committee meetings on Thursday, board member Tom Downs questioned whether a recent decision to extend service to Largo was the most cost-effective way to deal with one safety-related issue.

Metro officials originally envisioned making the Stadium-Armory station the eastern terminus for Silver Line service. But concerns about whether the turnaround near that station can be retrofitted to meet new safety standards prompted officials to announce that eastbound service would be extended to Largo.

That shift and other changes related to the start of the Silver Line — which will extend Metrorail service westward in Northern Virginia — is expected to cost an additional $4.6 million in the first year

Offering what he called a rough guess, Sarles said retrofitting the section of pocket track that would be used for the Stadium Armory turnaround — if it could even be done — might cost more than $300 million.

In other business, members of the Finance and Administration Committee were told that revenue from Metrorail is down by $4.1 million because of a decline in ridership.