The idea was complicated, but the need seemed clear: a see-through wall between the BART tracks and the platform to block people from jumping, falling or throwing items onto the tracks.

Doors in the wall would slide open only when the train pulled in.

Transit officials spent $1.4 million in Measure RR bond money to study the concept in 2017. The barrier would resemble that of an airport people mover — with doors that are closed when the tracks are empty, and open to let people into the train once it arrives. Originally, BART wanted to award a contract next year and have a pilot version in place at Oakland’s 12th Street Station by 2025.

But Wednesday night, BART’s general manager put the project on pause. He cited the complexity of BART’s changing fleet, and its transition to a new train control system, along with the challenge of adding a wall system in a station that’s already built.

“We wanted to study whether you could make a platform screen door system work with all those variables, and we put together a team of creative, innovative engineering types who were very excited to create a unique, one-off system for BART at 12th Street,” said Assistant General Manager Tamar Allen.

Then new GM Bob Powers came in. He and other top brass decided that “it didn’t make practical or fiscal sense to do that,” Allen said. She said the system, which would have been designed to work with a hodgepodge fleet of two- and three-door train cars, would have cost up to $24 million to build. It would have become obsolete when BART switches to a new train control system.

Still, BART is committed to doing the project eventually, after it secures a contract next year for a train control system that’s designed to communicate with platform screen doors, and swaps its old train cars for the Fleet of the Future.

Some directors couldn’t hide their disappointment after Powers sent out a memo Wednesday night saying BART officials had set the project aside.

“In my view, the platform screen door was a win-win-win,” said Director Robert Raburn. He pointed to the various advantages of the infrastructure, which would inhibit suicides, dampen sound at some stations — particularly the ones next to freeways — and allow BART to run a bullet-style service in which some trains blast through stations at 75 mph without stopping. The agency can’t do that when people are packed against the edge of a platform, Raburn said. He added that the idea “is not dead.”

“It will keep the tracks cleaner,” Board President Bevan Dufty said of the proposed platform doors. “It will be more difficult for people to urinate on the tracks. It will be more difficult for people’s phones to fall on the tracks.”

Notably, it would reduce the number of people stepping onto the tracks, which rose from eight incidents last year — six of which were fatal — to 14 incidents and six deaths this year, as of Tuesday. Commuters sat marooned Tuesday morning while police rescued another person from the tracks near Civic Center.

Agency managers have largely downplayed the barrier’s function in preventing people from jumping on the tracks. Instead, they’ve focused on other benefits, like keeping the tracks cleaner and boosting crowd capacity on the platform. Crowding will become more of a problem when BART beefs up its fleet and starts running 30 10-car trains per hour through the Transbay Tube, instead of 23 trains of varying lengths.

BART has no timeline for the project, though Allen acknowledged that it will probably be built after 2025, probably in a station that can “absorb the risk,” like one of the extension stops in San Jose. The agency has no cost estimates, though Allen believes the door system would cost less than $24 million.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan