San Francisco’s controversial red-painted transit lanes are beloved by many Muni riders, and the city’s transportation planners. But they’re not necessarily here to stay.

The crimson lanes are, as the saying goes, only a test.

Results of the test are still being gathered, but federal transportation authorities are expected to rule within months whether the bright-red pavement can stay or whether the city will have to remove it and live with drab but conformist white lane markings and signs.

Officials with the city’s Municipal Transportation Agency gained permission from state and federal authorities in 2012 to color some street pavement red to make transit-only lanes more visible and to try to persuade car and truck drivers to stay out of them. New York and other U.S. cities are also experimenting with red lanes. San Francisco’s are not actually covered in paint, but rather an acrylic pavement treatment applied in sheets.

Beginning in 2013, the MTA tested the idea on a short stretch of Church Street before rolling out what it calls “red carpet lanes” on stretches of other thoroughfares where heavy traffic causes delays for transit: Market, Geary, Third, O’Farrell, Haight, Judah and, perhaps most controversially, Mission between 14th and Randall streets.

In total, 17 San Francisco streets with existing transit-only lanes were approved for the red pavement test, as well as three that didn’t have reserved bus lanes. Not all of the stretches have yet been covered with red.

“We shared our citywide plan with (state and federal officials) and they gave us the green light,” said MTA spokesman Paul Rose.

But the experiment was supposed to last just two years, and involve periodic progress reports to the California Traffic Control Devices Committee and the Federal Highway Administration. The MTA’s first written report to the state agency, however, was not presented until Dec. 12.

With no firm deadline, the test continued mostly unnoticed, at least until it got the attention of Glenn Urban, who owns a car wash with his brother on Geary Boulevard in the Richmond District where the MTA plans to install red transit-only lanes as part of a bus rapid transit project now being designed.

Urban considers the red lanes a threat to businesses — including his — because they confuse drivers and dissuade them from crossing through them, even when it’s permitted. And that could lead customers to keep driving instead of stopping.

“When they see them, they don’t know what to do, so they stay away,” Urban said. The MTA, he added, has “done little research on what this red paint means to businesses.”

Urban pressed the issue with the state committee, convened by Caltrans, hoping it would end the experiment — and the red lanes.

But at a Dec. 12 meeting in Sacramento, the committee received the MTA report. It allowed the experiment to continue and ordered up a final report to the federal government due in March, said Duper Tong, chief of the Caltrans office of traffic engineering and a committee member.

The report, which focused on the Third, Geary and O’Farrell lanes, concluded that the colored pavement kept more cars out of the transit lanes and reduced collisions. It also slowed traffic outside the transit-only lanes but sped up buses only some of the time.

Transit-lane violations on Third Street, where the lanes were red, dropped by 51 percent, the report found. Total collisions on the three streets combined dropped by 27 percent. While traffic travel times increased from four to six minutes and transit travel times rose on O’Farrell and Third streets during evening commutes and on Third Street in the morning, commute times declined on Geary in both the morning and evening.

The spread of the red lanes has been controversial in some cases. When the MTA painted Mission Street red through the heart of the Mission District last spring, it installed forced right turns and banned left turns, and eliminated some street parking, and merchants complained that it was killing business.

“There are a lot of merchants that are not happy with all the changes on Mission Street,” said Phil Lesser, head of the Mission Merchants Association.

The association is not opposed to the red lanes, he said, because merchants want speedier buses to bring business to the Mission. But they want the MTA to provide public parking to mitigate what was lost and to make it simpler to navigate the maze of transit-only lanes and forced turns.

The MTA, he said, neglected the interests of the merchants in its quest to speed up Muni.

“The MTA did everything to accommodate red lanes and nothing to compensate,” Lesser said.

MTA officials have said they’ll look at changes to help merchants but that they aren’t considering eliminating the red lanes.

Transit riders want them to stay — in the Mission and elsewhere. They say the lanes cut time off of bus rides and make Muni much more reliable.

Andy Bosselman, a writer and transit advocate, says a red lane on Haight Street has improved his commute noticeably.

“It allows buses to be sped up by several minutes.” he said. “I love it. I take the bus a lot more frequently now because the red carpet lane makes that segment a little less gnarly.”

In considering whether to make the red lanes permanent, state and federal traffic officials will put an emphasis on how effective the paint is at keeping cars out, whether it reduces collisions and how much it speeds up buses, Tong said.

“Hopefully in 2017,” he said, “we will have some kind of resolution to the experiment.”

Michael Cabanatuan is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter:@ctuan