Most counties in California have local road systems that are at risk of failure due to deteriorating pavement conditions and other delayed upkeep, a new report concludes.

Sonoma County, which has struggled to fund road maintenance, is included in the "at-risk" group, while Mendocino and Lake counties were found to be even worse off, receiving "poor" marks for pavement condition.

Statewide, the 10-year maintenance backlog amounts to an $82.4 billion shortfall — equivalent to a 56-cent per gallon gas tax increase, the study found.

It does not call for any particular method to boost revenue for road upkeep, but concludes that without additional money, replacement costs will soar and "California's local streets and roads will continue to deteriorate rapidly within the next 10 years."

The report was released Tuesday by groups representing California counties, cities and transportation agencies and interests.

The report, issued every two years, is part of a push by local governments for additional state and federal road funds.

The latest survey found that unmet needs for local roads, bridges and other street infrastructure statewide have grown by nearly $4 billion, or almost 5 percent, since 2010.

Just to keep county and city road surfaces in their current state would require a nearly 150 percent increase in annual funding, from the current level of $1.3 billion to $3.2 billion, according to the report.

California counties and cities own and maintain 81 percent of the state's public roads, a network valued at $189 billion.

Sacramento supplies about 59 percent of funds for pavement work on local roads, mainly through gas taxes. Federal funds kick in about 10 percent and local governments supply about 31 percent, according to the report.

It found that the overall pavement condition for local roads statewide has not changed since 2010. On a scale of zero (failed) to 100 (excellent), the average score remains at 66.

But long-term pavement repair needs have still jumped by about $1.9 billion, to a new total of $72.4 billion over the next 10 years, the report concluded. Combined with needs for bridges, sidewalks and other local road infastructure, the long-term needs are $107.2 billion, with only $25.1 billion in funding.

Forty-four counties, including Sonoma, are now in the "at-risk" category, with pavement conditions ranging from 50 to 70. Sonoma County's rating was 50, the same as in 2010.

The report included city streets. Roads in unincorporated Sonoma County have consistently scored among the worst in pavement condition in the nine-county Bay Area. The county has estimated its 10-year shortfall for road repair at $920 million. Including city streets, the total shortfall for Sonoma County is $1.6 billion, according to the study.

Yet Mendocino and Lake could be worse off. They were among the seven counties with "poor" pavement conditions of zero to 49 in the statewide study. Mendocino scored a 37 — second worst in the state behind Amador County — and Lake County roads got a score of 40.

The long-term shortfall for Mendocino County, including cities, was reported as $617 million. It was $450 million for Lake County.

The seven counties given a "good" road condition score — between 71 and 80 — were Sierra, Nevada, Placer, Contra Costa, Santa Clara, San Mateo and Orange, which had the highest ranking of 77.

The report is sponsored by the California League of Cities, the California State Association of Counties, the Metropolitan Transportation Commission and other transportation interests.