After nearly 50 years, BART is retiring all of its legacy train cars and is now seeking ideas from the public to find new use for an undetermined number of them.

Last week, the public transit agency launched an official call for proposals through a newly released pre-qualification application process, marking "the first phase of the project to donate legacy fleet cars to the public," officials said in a statement.

BART said it is "giving museums, nonprofits, agencies and the general public a chance to extend the lives of decommissioned train cars in creative and innovative ways."

Most of the retired train cars -- many of them dating back to 1972 -- will be recycled and used for parts, including wheels, axles and traction motors that can still be used to maintain BART's existing fleet. A total of 775 new Fleet of the Future cars will replace the old trains.

While ideas like sinking retired carbon steel subway cars into the ocean as part of an artificial reef have been tried, officials said the aluminum composition of BART cars "prevents this from being feasible."

Likewise, BART also operates on a "non-standard gauge or track width that wouldn't work in most places," making selling off the cars to be reused by other systems less possible.

Pre-qualified applicants will advance to the next phase of request for proposals. Those who present viable proposals will have as many cars as they request made available.

Some key criteria for obtaining a legacy car include "the project must not cost BART any money once the car has been prepared for delivery." Selected applicants must pay the costs of transporting the train car from BART's property to their own (including flatbed truck and crane rental), which is estimated to cost $8,000 to $10,000 per car.

"It is important to us that the future of these cars continue to be a great representation of BART and that their use is appropriate. We've developed these guidelines for anyone interested in purchasing the cars," officials said.

A project selection committee will review applications and select proposals that meet all required criteria, including a final disposition plan once the project is completed.

Notifications for successful pre-qualifications will be sent in June, with awards of proposals scheduled for December and the first cars being transferred to awardees in 2022.

The application system is located at bart.gov/legacycars. Applicants are encouraged to review the "Pre-Qualifications for Proposals" brochure about the proposal process, timeline and car measurements before submitting.

The pre-qualification applications deadline is March 12 at 5 p.m.