People aboard a Red Line train in Rockville. (Katherine Frey/The Washington Post)

Metro needs to improve the methods it uses to decide how to spend more than $1 billion a year for capital projects, because it doesn’t fully assess which projects are most necessary for system safety, according to a new federal study released Thursday.

The report, by the Government Accountability Office, found that Metro fails to follow industry best practices, such as scoring and ranking projects before choosing which to do first.

Metro also lacks a complete inventory describing the condition of its physical assets, including track, tunnels, bridges and communications equipment, the study said.

And although the GAO found that Metro has made significant progress in reducing incidents caused by track defects and electrical fires, it has not adequately studied the risk posed by non­electrical track fires, which account for nearly a third of all fires in the system.

Metro accepted most of the recommendations contained in the 56-page report but said it has already upgraded many of its practices and needs more time to finish the process.

The study, which was requested by the Washington region’s U.S. senators, is expected to help them craft conditions for Metro to satisfy in return for getting a 10-year extension of a federal program that provides the agency with $150 million a year.

Democratic Sens. Mark R. Warner and Tim Kaine of Virginia and Ben Cardin and Chris Van Hollen of Maryland signaled that they are close to proposing legislation to extend the program that expired last year.

“We plan to give this [GAO] information careful consideration as we move forward to introduce important [Metro] legislation in the coming weeks,” the four said in a joint statement.

“As their audit found, putting in place clear project ranking methodology, measuring program performance, and developing an accurate inventory of assets will all be critical to improving performance of the Metro system,” the statement said.

The GAO looked at how Metro spent its capital dollars — money spent to buy new rail cars, buses and other equipment, and to modernize and rehabilitate the system — from 2011 through 2017. Metro spent an average of $845 million a year on capital projects during that period, which included the January 2015 L’Enfant Plaza smoke incident that left one passenger dead and many more injured.

The senators requested the study in part because that calamity prompted Metro to undertake an emergency rehabilitation project and increase its capital spending, both to guarantee safety and improve reliability. The lawmakers want to ensure the money is being spent effectively.

Metro’s capital spending is projected to rise to $1.3 billion in this fiscal year, which ends June 30, and to continue at well above $1 billion a year in coming years. That’s possible partly because the District, Maryland and Virginia reached a landmark deal last year to provide the transit agency with $500 million annually in dedicated funding.

The GAO said Metro needs to adopt more rigorous and systematic processes for evaluating which capital projects to prioritize.

Four out of five peer transit agencies consulted by the GAO said they use a project scoring and ranking system to decide where to invest, and the fifth is planning to do so — but Metro hasn’t got there yet.

“Without a documented planning process that includes procedures for ranking and selecting projects for funding in the fiscal year 2020 capital budget, [Metro’s] stakeholders lack reasonable assurance that [its] capital investment decisions will be made using a sound and transparent process,” the GAO said.

The report also faulted Metro for lacking “a complete inventory or physical condition assessments of its assets.”

It said Metro’s preventive maintenance program has succeeded in reducing electrical wayside fires and track defects by 50 percent from 2017 to 2019. But the program does not specifically address nonelectrical fires, such as those caused by rail cars or debris, and the number of those fires remained steady at 23 in both 2017 and 2018.

Metro’s responses were included in the GAO report. A Metro spokesman issued a short response, as well, saying, “In the two years since the request for this report, Metro has made significant progress and taken actions to address several of the report’s recommendations.”

He continued: “We look forward to working with our partners in the region’s congressional delegation as we continue to undertake capital investments to improve the safety, reliability, and fiscal sustainability of our system.”