Fresh from winning voter approval of a $3.5 billion bond measure, BART is looking at asking for another $1.5 billion as part of a bridge-toll increase that could go on Bay Area ballots as early as next year.

The idea being pushed by BART and other transit agencies is to raise tolls on the Bay Area’s seven state-owned toll bridges — that’s every one of them except the Golden Gate — by $1 to $3. Officials are still haggling over the exact amount, but the upper range would boost the top cost of crossing the bay in a car to $9.

The full list of transit projects that would get the money isn’t finalized. But BART is already planning to push its way to the front of the line and ask for as much as a third of the toll dollars that the measure would generate.

It was just three months ago that BART won a high-stakes campaign to persuade voters in Alameda, Contra Costa and San Francisco counties to approve Measure RR, a bond issue that will pay for a host of nuts-and-bolts improvements to the nearly five-decade-old system. This next ballot bid would be called Regional Measure 3 and would go before voters in all nine Bay Area counties, probably in 2018.

“Rebuilding our transportation system is similar to maintaining a house — it’s really never done,” said Randy Rentschler of the Bay Area Toll Authority, which would have a major say over how the money raised by the new measure would be divvied up.

BART says what it needs most is 306 additional railcars. There’s no money in Measure RR to pay for them, and they’ll cost a lot of cash — $1.6 billion, to be exact.

BART hopes $1 billion of that will come from the envisioned toll-increase measure, which would still leave it $600 million short of what it needs for all the cars. That money would have come from sales-tax hikes on the November ballot in San Francisco and Contra Costa counties, but voters there fouled up BART’s plans by rejecting the increases.

The 306 new railcars BART hopes to purchase are on top of the 775 already on order as part of the replacement of its aging fleet.

Other BART priorities for the toll money include $250 million to modernize train control and traction power systems and $90 million to design a seismic retrofit of the 3.6-mile Berkeley hills tunnel.

Also on the list is $120 million to pay for “capacity enhancements” at the heavily used Embarcadero and Montgomery Street stations in San Francisco. BART would use half the money to install automated sliding glass doors on the platform that would keep riders safely separated from the tracks, and the other half to add elevators, escalators and stairs.

None of this can happen until the Legislature gives the OK for Bay Area voters to decide on a bridge-toll increase. State Sen. Jim Beall, D-Santa Clara, is expected to introduce legislation that would do that, according to those following the process. Beall’s office declined to comment Tuesday.

Bay Area voters last approved a $1 increase on local toll bridges in 2004, to pay for congestion-relief measures. Transit officials have since imposed two $1 toll hikes on their own, for bridge seismic retrofits.

Measure RR in November was no easy sell, because BART had to persuade two-thirds of voters to give the thumbs-up to pass it. A toll hike wouldn’t be as big a challenge — it would require only a cumulative simple majority in the nine Bay Area counties.

BART wouldn’t be the only transit agency benefiting from the toll hikes. Money probably would also be spent on ferries, express buses, high-occupancy-vehicle lanes and even the new Transbay Transit Center in San Francisco, which has already received $300 million in toll revenue.

As for justifying BART’s grab of toll dollars, transportation officials argue that the rail system carries an average of 28,000 people each weekday rush hour — nearly twice the number that move in cars over the bay.

“This is very real congestion relief, which is capacity improvement,” said Nick Josefowitz, a BART Board of Directors member from San Francisco who helped lead the campaign for Measure RR.

According to BART spokesman Jim Allison, the bond measure that voters approved in November covers a bit less than half the cost of a new, $915 million train control system that will allow 30 trains an hour to travel under the bay, six more than now.

But a bit less than half isn’t enough — which is why BART is extending its hand to voters, again.

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call (415) 777-8815, or email matierandross@sfchronicle.com. Twitter: @matierandross