The price of California gasoline, already the highest in the nation, is set to go up more than 5 cents a gallon just in time for your summer vacation.

“It’s crazy. Ridiculous. And it’s not like you can say the roads are getting a whole lot better,” said Marcia Stuerner, as she paid $3.89 a gallon at the Chevron station at Sixth and Harrison streets in San Francisco.

The 5.6-cent-a-gallon bump starts July 1 and comes on top of the 12-cent-a-gallon tax hike that went into effect Nov. 1, 2017.

The July gas tax hike will be followed by ongoing annual 2% to 3% hikes in the tax to adjust for inflation.

“That’s about 1.5 cents a gallon rise annually, every year going forward,” Metropolitan Transportation Commission spokesman Randy Rentschler said.

Motorists at the Chevron station weren’t happy with the latest price increase, but said they have little choice but to suck it up and pay up.

“What are you going to do? You can’t live without gas,” customer Andrea DeFrancesco said.

Rentschler said the higher gas taxes are expected to generate $5.2 billion statewide each year to repave highways, fix dilapidated bridges, fill potholes and beef up public transit systems like BART.

“While not to anyone’s liking, this is medicine long overdue and desperately needed, as too many Bay Area roadways are well past middle age and are declining every year,” he said.

The gas tax hike comes on top of Regional Measure 3, which upped the tolls by a dollar on the state’s Bay Area bridges to pay for transit improvements as well.

Democratic state Sen. Steve Glazer of Orinda, who was a “no” vote on the gas tax hike, said the ongoing increases are “just going to make it that much more expensive for lower-income families who live here.”

The July boost was contained in the fine print of the gas tax package approved by state lawmakers in 2017 and reaffirmed by voters when they rebuffed a call to repeal the tax last year.

The July bump is the latest price rise in California, where the price at the pump is already about $1.25 more per gallon than in other states.

Part of the higher cost is the initial 12 cents per gallon gas tax increase that went into effect last November and now rises to 17.6 cents a gallon.

“Then there are the fees to address environmental impacts, mostly climate change,” said Severin Borenstein, faculty director of the Energy Institute at UC Berkeley's Haas School of Business.

The state’s cap-and-trade program on greenhouse gases added 12 cents a gallon in 2018. The state’s “low carbon fuel standard” fee has pushed the cost of a gallon of gas up by about 14 cents.

“Finally, we pay 2 cents to clean up old gas station sites where fuel leaked into the soil,” Borenstein said.

For a total per-gallon cost near $4 that includes $1 in federal and state taxes and fees.

“A slice of the remaining difference pays to refine oil so that it meets California’s cleaner-burning gasoline formula, but most analysts think that the cleaner formulation adds no more than 10 cents to what we pay at the pump,” Borenstein said.

Then there’s what Borenstein has labeled the “mystery surcharge which occurs between the refinery and the pump and started showing up within the industry in February 2015 after a refinery fire in Torrance (Los Angeles County) drove up the price of gas.

But unlike past years when shortages prompted price spikes that soon fell back, the 2015 hike stayed in place and grew to about 50 cents a gallon this summer.

There have been repeated calls for the attorney general to investigate what’s behind the mystery price rise.

The attorney general, however, will neither confirm nor deny any investigation is in progress.

The AG’s press office, however, did say that they are aware of, and monitoring, a recent spiking of gasoline prices in response to refinery outages.

Whatever the case, so far no one has been able to pin down the reason behind the charge, which Borenstein estimates has cost California drivers about $20 billion to date.

Happy motoring.

San Francisco Chronicle columnist Phillip Matier appears Sundays 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 pmatier@sfchronicle.com. Twitter: @philmatier