The Metro board voted Thursday to provide funding to double Red Line service for Shady Grove, but the transit agency said it is unsure its infrastructure can handle the extra trains.

For years, Metro has been turning back about half the Red Line’s outbound trains at Grosvenor and Silver Spring during rush hours to better serve the downtown core. The practice was initially started because of a shortage of rail cars.

But Montgomery County residents and elected officials have been lobbying to end the practice to ease the commute for riders on the western end of the Red Line by providing them with more frequent service.

Metro is studying whether the system can handle 15 trains an hour at Shady Grove, a $2.5 million a year proposition that would provide the best-case scenario for those riders. The agency could also partially eliminate the turnback — sending 12 trains per hour to Shady Grove at a cost of $1.6 million. (In a third scenario, Metro would not adjust service at all). The study is due in July.

The budget amendment approved Thursday provides $1.25 million to restore full service at Shady Grove through next June, but Metro says it is awaiting the July study to determine how many more trains the system can reliably handle. The board will then decide whether to eliminate the turnback by January.

Thursday’s vote follows up on a 2015 resolution that instructed the agency to end the practice by this summer.

“Ending the Grosvenor turnbacks has been a long-standing objective for improving service for Maryland Red Line riders for both Montgomery County and the state of Maryland,” board member Michael Goldman said. “Maryland [was pledged] the ending of the Grosvenor turnbacks when sufficient new 7000-series rail cars were available to permit the added trains. . . . Deliveries were on schedule and so it can happen this fiscal year.”

Under current service levels — seven to eight trains per hour — riders at Shady Grove face packed conditions and waits of at least eight minutes, compared with four minutes for those closer to the center of the line. The changes would raise service levels by up to double.

A Metro analysis has concluded, however, that increasing service levels could require new capital investments, such as an added crossover, totaling $20 million to $30 million, according to board members who cited memos provided to the panel.

Board member Steve McMillin cited the cost and potential long-term investment in opposing the budget amendment at a meeting of the panel’s finance committee.

“The benefits [are] relatively few in terms of virtually no additional ridership, virtually no additional revenue,” said McMillin, who represents the federal government. “I don’t feel that given that overhang on our already stressed capital budget that this is a wise commitment for the board to make at this time.”

Despite federal board members’ objections, however, the resolution passed the committee and later was approved by the full board, with McMillin dissenting.

Goldman, who represents Maryland, cited figures from Montgomery County that show new development between White Flint and Shady Grove would result in thousands of new riders who would benefit from the added service.

“If trains start at Shady Grove at rush hour, on-time performance will improve, riders will enjoy a less crowded experience, Metro will have a more efficient service and we’ll save money thereby,” Goldman said.

Goldman pointed to a Metro staff analysis from April 30 that showed every train leaving from Shady Grove between 7:47 and 8:47 a.m. had more than 100 passengers on board by the time it got to Grosvenor. Further, the study took place on a Monday, when ridership is lighter than normal.

“These are very crowded trains,” he said. “This results in uneven passenger loading, longer station dwell times and a poorer experience for passengers than on those boarding trains at Grosvenor.”

Because the budget amendments also provide $3.7 million for bus service changes that go into effect before the end of June, the board was forced to hold a special meeting immediately following the finance committee to approve the measure. The provisions include funding to make Rhode Island Avenue’s G9 express route permanent and support the addition, modification or elimination of two dozen bus routes under the agency’s annual bus realignment.

Metro Board Chairman Jack Evans said the agency’s upholding its commitment to Maryland reflected a “spirit of regional cooperation” in the wake of the historic agreement to provide Metro with $500 million in annual dedicated funding.

“In the best of all worlds you’d wait until the study’s done before you did the financing, but in the situation we’re in now,” Evans said, “I don’t want to send the message to Maryland that one of their top priorities — we’re not necessarily interested in doing.”

He said the funding commitment was minimal, joining Goldman who said the $1.25 million represented a “picayune amount” when held up against the agency’s $1.8 billion operating budget.

“It’s only a small amount of money that continues to keep the project moving forward,” Evans said. “An analysis will be done and we’ll come back and if it makes no sense, then we’ll have a different approach at that point in time.”