When the price of gas went up 12-cents last week, thanks to a Democrat-backed state transportation bill, California Republicans responded with reproachful head shaking and murmurs of concern for those who will be paying higher prices.

“We’re overburdened with taxes in California,” said Sue Caro, chairwoman of the Alameda County Republican Party and a state party official. “This just makes life more expensive, especially for low- and middle-income residents and seniors.”

But behind the scenes there was likely backslapping and high fives as GOP officials beamed at the prospect of putting a gas tax repeal initiative on the November 2018 ballot that could bring out droves of tax-hating Republican voters.

In a state where GOP registration is falling fast, Republicans are shut out of statewide offices and half the party’s Congress members are being targeted by anti-Trump Democrats, GOP leaders are fighting for any edge they might get, and the gas tax might be their best shot.

The SB1 transportation bill, along with the $5.2 billion in annual taxes and fees it authorized, is “a #Gastaxtrophe,” they proclaimed.

“Thanks to Gov. Brown and the out-of-control California Legislature ... every California commuter will be reminded how Sacramento’s failure to govern directly impacts their pocketbook,” Jack Pandol, a spokesman for the National Republican Congressional Committee, said in a statement Wednesday. “California families living paycheck-to-paycheck will hold Democrats accountable for this regressive tax on the poor.”

But those GOP complaints are more about hardball politics than any concern for California voters and the needs of the state, said state Sen. Jim Beall, D-San Jose, the author of the transportation measure.

After more than four years of study, hearings and negotiations on the state’s road and transportation needs, “the people who reviewed the information on a factual basis, we convinced,” Beall said. “But the people who reviewed it based on political considerations, we didn’t.”

For Beall and the Democrats who pushed the bill through the Legislature and narrowly got the needed two-thirds vote, the decision was a no-brainer. Not only hadn’t the state increased the per-gallon gas tax since 1994, the fuel efficiency of cars and trucks also has improved substantially, which means people are going farther on less gas — and paying less in gas taxes.

The new transportation bill not only boosts the gas tax, but also adds 20 cents to each gallon of diesel fuel, increases the diesel fuel sales tax by 4 percent, raises the vehicle registration fee and, beginning with the 2020 model year, requires owners of electric cars and other zero emission vehicles to pay an annual $100 road improvement fee in lieu of the gas taxes they don’t pay.

That adds up to $52.4 billion in new transportation money that will go to the state and local governments over the next 10 years for road and bridge improvements, with some of the money earmarked for mass transit, and bike and pedestrian paths.

Supporters of the transportation bill say new taxes are the only way to provide the money needed to pare down what transportation officials say is a $59 billion backlog of highway repairs and $75 billion for work on local streets and roads.

“Some people want to oppose this for their own political purposes,” said Michael Quigley, executive director of the construction-friendly California Alliance for Jobs and a leader of Fix Our Roads, a coalition of supporters of the transportation bill. “But most people realize the gas tax is a users’ fee and ultimately represents a good thing for them, the roads and the state.”

Two separate GOP-friendly groups already are pushing measures for the November 2018 ballot that would repeal the various transportation taxes and fees, but both are still awaiting the final OK from the state before they can begin to collect the hundreds of thousands of signatures needed to qualify for next year’s ballot.

California Republicans see the gas tax repeal as a welcome oasis of opportunity in what’s otherwise a GOP political desert. With two little-known Republican candidates, San Diego-area businessman John Cox and Assemblyman Travis Allen of Huntington Beach (Orange County), currently in the race for governor, there’s a chance that a pair of more visible — and far better financed — Democrats could finish first and second in June’s top-two primary and crowd out the GOP at the top of the November ballot.

But even with a Democrats-only governor’s race, a hot battle over the gas tax could bring out Republicans and anti-tax independents who would also vote for down-ballot Republican candidates, such as the seven GOP members of Congress now being targeted by Democrats.

That prospect has led to bruising tactics on both sides. GOP opponents of the gas tax already are pushing to recall state Sen. Josh Newman, D-Fullerton (Orange County), who won a Republican-held seat last year and then voted for the transportation bill.

In September, the Fix Our Roads group, which includes not only labor, construction industry and local government representatives, but also business-oriented groups like the California Chamber of Commerce, sent a letter to the 14 GOP California members of Congress, warning them to stay out of the gas tax fight since “with so much at stake, our organizations will have no option but to mount a robust and powerful effort in opposition to this initiative, using the voice of the California business community to counter your efforts.”

But 11 of those GOP congressmen quickly sent a letter saying they would back a repeal of the new taxes and fees, betting the stand would bolster their support next year.

Republicans and other opponents of the gas tax don’t say road repairs aren’t needed, but argue that SB1 isn’t the way to go.

“California keeps receiving more tax revenue, more than enough to fix our roads and expand our freeways without raising taxes a dime,” said Allen, the Orange County assemblyman who wrote one of the repeal initiatives.

“The argument that we need money for roads is absolutely correct,” but the Democrat-led Legislature shouldn’t be able to vote new taxes in on their own, said Jon Coupal, president of the anti-tax Howard Jarvis Taxpayers Association who backs a competing repeal effort. “What we’re saying is that changes like this have to go to the voters.”

Democrats and other supporters of the transportation bill are doing what they can to ease the impact — and the visibility — of the new fees. For instance, the gas tax took effect Nov. 1, the day oil companies can begin pumping the less-expensive winter-blend gasoline. And with gasoline prices being as volatile as they typically are, the extra 12-cents could quickly disappear into the usual ups and downs of pump prices.

Republicans also should be worried that get-out-the-vote efforts work in both directions, especially with supporters of the transportation bill ready to spend $30 million or more to fight off repeal, said Rob Stutzman, a GOP consultant working with Fix Our Roads.

“People don’t like taxes, but it’s a trade-off, since if you cut the taxes the road repairs go away,” he said. “And to beat back the repeal, supporters will spend a lot of money turning out Democrats.”

And while any repeal measure won’t be on the ballot for a year, the state and cities already are filling potholes and repaving roads with the promise of new state money. It’s a safe bet that for the next 12 months transportation officials across California will be reminding voters just where the cash for those repairs is coming from.

“It’s not taxes we’re supporting, but the results, the outcome,” said Quigley of the California Alliance for Jobs.

John Wildermuth is a San Francisco Chronicle staff writer. Email: jwildermuth@sfchronicle.com Twitter: @jfwildermuth