Motorists are paying a hidden tax for bad roads.

Vehicle repairs attributable to potholes and crumbling pavement cost hundreds, in some places thousands, of dollars a year above and beyond routine maintenance.

San Francisco and Oakland top the list of America’s major metropolitan areas with an average of $1,044 a year in extra repairs, according to a transportation research group called TRIP. Sonoma County ranks No. 5 among communities with 250,000-500,000 residents at $841 a year.

California isn’t the only state with lousy roads, but it dominated TRIP’s lists of cities with poor pavement and steep auto repair bills, followed (at a distance) by Texas and Michigan.

More than a quarter of the nation’s major roads are in poor condition, according to TRIP, which warns in a report called “Bumpy Roads Ahead” that deterioration will accelerate as vehicle travel returns to pre- recession levels.

That in turn translates into even larger bills for avoidable repairs.

Gov. Jerry Brown alluded to that when he called the Legislature into special session to address the deplorable condition of California’s streets and highways. “If you’re roof is leaking,” he said, “you better plug it up or you’re going to pay more later.”

That was in June, and there have been few signs of progress.

Legislators reconvene Monday after a month-long recess. If they spent any of their summer vacation on California roads, perhaps they will return to Sacramento with a renewed commitment to filling potholes (along with a realignment or a new set of tires).

What we’ve seen so far is posturing along predictable lines. Democrats are focused on fuel taxes, which haven’t increased in decades. Republicans are pointing at bureaucratic bloat, especially at Caltrans. Cities and counties, which are heavily dependent on Sacramento for revenue, are angling for a piece of the pie.

All of these warrant serious consideration.

California’s last gas tax increase was approved by voters in 1990 — a quarter-century ago, before electric cars and hybrids and many improvements in fuel efficiency. Inflation, meanwhile, has driven up the cost of construction, with the Congressional Budget Office saying that real spending — federal, state and local — on road repairs peaked in 2002.

The GOP wish list includes a share of cap-and-trade money for road repairs, restrictions on permanent hiring at Caltrans, exempting road repairs from environmental review and appointing an inspector general to investigate Caltrans and the high-speed rail program.

This past week, cities and counties (joined by a group representing heavy equipment operators and construction companies) called for $60 billion in new revenue over 10 years, divided equally between state and local governments.

Their plan would bring $25.5 million a year into Sonoma County, half earmarked for the county and half divided among the nine cities, with potential revenue sources including fuel taxes, higher vehicle license fees and a new user fee for electric vehicles and vehicles that don’t use fossil fuels.

There’s something here for everyone to hate, but California’s roads are only getting worse, and lawmakers should bear in mind that, if roads are improved, any new taxes would be at least partially offset by fewer auto repair bills.