SAN JOSE — Drivers are already painfully aware that San Jose has too many potholes, but a startling new audit has found that a decade of pavement neglect has left city streets deteriorating toward the ranks of the worst roads in the Bay Area.

And the taxpayer cost to fix the problem is eye-popping: half a billion dollars.

The independent city auditor’s six-month investigation found that in a few years, 38 percent of local San Jose roads that are currently fine to drive on will fall into “poor” condition, where cheap maintenance no longer works and visible spider-web cracking makes for a bumpy ride. Adding to roads that are already in rough shape, by the end of the decade 61 percent of all local streets are forecast to be in lousy condition, putting San Jose on par with the likes of Richmond, Vallejo and East Palo Alto, dropping far below San Francisco and Oakland and remaining better than only a few, mostly rural Bay Area towns.

The imminent flood of collapsing roads is the result of the city pulling funding for street maintenance over the last decade, spending money on only the most badly damaged main roads to compensate for other city realities — such as rising pension costs, sagging revenues and more urgent priorities like the shrinking police force. Once a typical road hasn’t been touched up in 10 years, it hits a tipping point and deteriorates rapidly, requiring construction that is three to five times more expensive than simple routine maintenance, the audit says. Now, the bill is about to come due.

“We are in danger of things getting much worse,” auditor Sharon Erickson said in an interview. While residential streets are the hardest hit, “we found that no neighborhood is immune.”

A City Council committee on Monday will begin the process of trying to figure out how to “get us out of the big pothole that San Jose finds itself in,” as transportation Director Hans Larsen put it, but there are no easy answers.

The city would need to triple its current annual spending on streets to $68 million a year just to keep roads in their existing condition, the audit found, because fixing failed roads is so much costlier than simply maintaining good ones. To actually improve all the streets, it would cost $504 million total — double the estimate from a half-decade ago and equivalent to the entire budgets for the Police Department, Fire Department and libraries combined.

The costs are so high because the city failed to take care of its roads earlier. With $1 million, the city could apply a new layer of asphalt to spruce up about 19 miles of streets in fair quality — but that same amount of money would only fix 1.3 miles of rough pavement and just a half-mile of a badly damaged road that needs to be rebuilt.

The city has forecast flat overall revenue for the coming years and actually has penciled in decreased spending on roads. But the audit is launching a rethinking of that strategy, with a hearing before the full City Council set for as early as late March.

Already, city transportation officials have suggested trying to get a bigger share of regional funds and have launched a public awareness campaign, putting on the city website a Google map where residents can look up the condition of their street. They’ve also once again floated the idea of asking voters to approve a city tax increase or huge bond next year.

“It’s likely that we’re going to need to go to the voters and ask them, is this a big enough priority for them?” said Councilman Ash Kalra, who chairs the Transportation and Environment Committee, which will begin examining the issue. “We need to act quickly to prevent even greater costs.”

Even before the coming onslaught of potholes, road repairs had already been the lowest-rated of any city service of San Jose, with only 28 percent of respondents in the city’s most recent annual survey rating them as good or excellent. By comparison, the Police Department, which has recently lost hundreds of officers and been hit with occasional high-profile crime surges, was rated favorably by 46 percent of survey takers.

San Jose already ranks last in Santa Clara County for road quality, and its average pavement score is 79th out of 109 Bay Area cities and counties, down from 51st a decade before, according to data from the Metropolitan Transportation Commission. The forecast outlined in the audit based on current spending would make San Jose 96th by 2020 and 104th by 2025, or last among cities south of the Golden Gate Bridge, if the other cities remain the same. On the way down, San Jose, already slightly worse than San Francisco, would drop below Oakland, Los Angeles and San Diego for pavement quality.

“If we do nothing, we’re essentially going back to driving on gravel roads,” Larsen said.

San Jose is in especially bad shape to fix its problem because it has such a sprawled-out population, with many residential streets serving few residents compared with other big cities. Yet despite the out-sized burden, the audit found San Jose only spends $27 per capita on its streets, lower than other big cities such as San Francisco ($47) and suburban neighbors like Santa Clara ($34).

About 140 California cities and counties have gotten voters to approve sales taxes and bonds to fix streets. While poll results last year showed a streets bond in San Jose would fail, city leaders are likely to reconsider a measure in November 2016.

“This is a really big problem,” Larsen said, “and we need to do something about it soon.”

Contact Mike Rosenberg at 408-920-5705. Follow him at Twitter.com/RosenbergMerc.