San Francisco officials are contemplating tolls to drive along busy arteries downtown, where traffic crawls so slowly that cars spend much of the journey sitting.

The county Transportation Authority board — also known as the Board of Supervisors — set aside $500,000 this week to study the idea and gather data on who drives downtown during rush hour and why. Still, one supervisor was skeptical, calling the fare a potential hardship for residents and businesses struggling to survive in a high-priced city.

“I don’t really dig it, it’s not my deal,” Supervisor Sandra Lee Fewer said of congestion pricing. She voted to fund the study anyway.

Officials haven’t quite nailed down their definition of “downtown,” which would probably include the SoMa and Financial District neighborhoods that link to the Bay Bridge. This eastern swath is among four areas in the city that could become testing grounds for pricing interventions.

The supervisors are also hemming and hawing over a proposal to charge $3.50 to enter and exit Treasure Island — which infuriates residents, even though transit officials say it’s necessary to prevent gridlock on the Bay Bridge. A third plan would impose fares of up to $10 on the crooked part of Lombard Street, the winding 500-foot brick roadway that draws 2 million tourists a year. And then there’s the possibility of tolled express lanes along Interstate 280 and Highway 101, connecting San Francisco to San Mateo county.

“This idea is taking off; it’s being studied everywhere,” said Stuart Cohen, executive director of the Oakland nonprofit TransForm, which presses for transportation policies that reduce fuel emissions and help impoverished communities.

Cohen pointed to New York City, which imposed a $2.50 surcharge on taxis driving on the traffic-snarled roads south of 96th Street and a $2.75 surcharge on ride-hailing services such as Uber and Lyft. Seattle and Vancouver are seriously considering such ideas.

The question, he said, is whether cities can add these fees without unfairly burdening low-income motorists. Members of TransForm say it’s possible. Earlier this month, the group published a report that lays out strategies for fair and equitable congestion pricing. The method works if cities pair it with big improvements to mass transit and bike lanes and aim to reduce solo driving that pollutes the air in poor communities, they said. The report also recommends a tolling system with discounts for low-income people.

Though the concept is catching on nationally, new fares tend to get residents riled up in San Francisco, and a recent Chamber of Commerce poll showed that respondents have little appetite for the added expense: 30 percent of people surveyed supported the idea of a $3 toll to drive into the northeastern part of the city; 65 percent said no, and the rest were undecided.

Supervisor Rafael Mandelman mentioned those results at the transportation board meeting Tuesday.

“There is inherently concern and doubt about this approach (of) charging to use our roads,” he said.

But, he added, “Our tools for dealing with the proliferation of Uber and Lyft are limited. One of the tools we have left is congestion pricing.”

Cohen expects support to grow if officials add the toll and it shaves half an hour off every car trip through SoMa.

“People can’t even conceive of a downtown where traffic flows,” he said.

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