Metro is seeking to privatize its parking facilities, a measure that would help boost revenue for the agency but may result in higher parking fees for customers.

In a request for proposals posted on Thursday, Metro officials said they’re seeking private companies capable of managing the agency’s 56 parking facilities — more than 59,000 parking spots — for a contract length as long as 50 years.

The company would pay to lease the parking facilities from Metro, providing either one large lump sum or a series of regular payments. In exchange, the company would be able to collect revenue from parking fees paid by passengers. The company would be responsible for managing parking operations, cleaning and maintaining the facilities, investing in capital improvements and providing customer service.

If the contractor wants to increase parking fees, it would need to get approval from the Metro Board of Directors. According to Metro’s document to potential contractors, officials say it would be reasonable to assume a 3 percent annual increase in the parking rates. The contractor would also have to get board approval to change the hours of operation for the parking garages.

Metro said the contractor would be “encouraged” to continue using SmarTrip cards as a means for people to pay the fee.

“[The Washington Metropolitan Area Transit Authority] is seeking a highly-qualified concessionaire which is well-capitalized,” Metro wrote in the document to potential bidders, “and has a proven track record of managing, operating and financing a complex portfolio of parking assets of similar type and scale to WMATA’s parking portfolio.”

Privatizing parking has been on the agenda for General Manager Paul J. Wiedefeld since he came to Metro nine months ago: In a letter to staff and customers released in March, he said that establishing public-private partnerships for parking operations and paratransit services could help the agency save a significant sum.

Members of the Metro Board have said in recent months that they’re eager to see Wiedefeld execute that plan and are likely to approve a contract for privatization.

The contractor will be selected based on technical and financial capacity, ability to provide high-quality customer service, and ideas for innovation — including dynamic parking prices and apps for customers.

Initial proposals are due Oct. 28. Metro plans to select a preferred bidder by the beginning of December.