A new transportation plan proposed by House Democrats would let King County voters impose a steep car-tab tax for transit and roads, while urban Snohomish County might vote on higher sales taxes for bus service.

King County Metro Transit has said it will cancel 65 routes and reduce service on 85 others without new sources of money. Some county roads are reverting to gravel.

Community Transit in Snohomish County canceled Sunday service in 2010 and reduced local weekday trips after the recession, when sales-tax revenue dipped. Agency leaders want to restore lost service.

In both counties, tax increases would require approval of voters, according to the plan released Tuesday by House Transportation Committee Chairwoman Judy Clibborn, D-Mercer Island.

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The local taxes would be in addition to a proposed 10 cents-a-gallon increase in gasoline taxes and higher car-tab fees that would finance state highway projects.

King County would consider a car-tab tax of as much as $150 per $10,000 of vehicle value, of which 60 percent would go to transit and 40 percent to roads and streets.

That translates to $86 million each year for buses, said Kevin Desmond, Metro general manager. About $75 million would prevent operating shortfalls, leaving some $11 million to add trips on popular routes.

Clibborn’s plan also would help bus riders in West Seattle, Burien and White Center. The state would contribute $17 million to sustain Metro bus hours that were added to help reduce traffic congestion caused by Highway 99 construction, until early 2016.

Ridership there has grown in the past two years, to about 24,000 daily boardings, says Metro’s “Keeping Seattle Moving” communiqué.

Tuesday’s proposal creates a dilemma for boosters: Depending on what the Legislature does, the statewide highway plan could appear on the ballot alongside county requests for local taxes.

“It becomes a tough issue for the general public to understand,” said Desmond. He acknowledged the county wanted the option of elected council members enacting a tax themselves.

Senate Transportation Committee Co-Chair Curtis King, R-Yakima, insisted on letting voters decide.

“My view is that they need to go to a vote of the people. That’s my first concern,” King said in an interview this month.

In Snohomish County, Community Transit could ask voters to raise its current sales tax of 9 cents per $10 purchase by as much as 3 cents more.

“The main thing is having the ability to make the case to our community for increased transit funding,” spokesman Martin Munguia said.

King County Metro will lose a $20 yearly car-tab fee that expires in mid-2014, as Highway 99 bus contributions run out and Metro spends down its previous $100 million surplus.

Those sources of money, along with fare increases totaling $1 since 2008, have averted big cuts at Metro so far.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com. On Twitter @mikelindblom