A politically powerful coalition is testing the appetite for a statewide sales tax to raise $600 million a year for road repair and construction and transit projects across Colorado.

MPACT64 — a group that includes the Metro Mayors Caucus, Progressive 15, Action 22 and Club 20 — is slowly rolling out the plan to place a tax question on the 2014 ballot and collecting a list of wants and needs from city councils and county commissions statewide.

So far, the reception has been mixed.

“We’ve certainly heard that transportation needs are a priority for many communities,” said Metro Mayors Caucus director Catherine Marinelli.

But the details of the proposal are still vague, said Westminster Mayor Nancy McNally, a member of the transportation-focused MPACT64 coalition, which includes members from the state’s 64 counties.

“Right now, we really don’t have anything to talk to them about, so I don’t know yet what the answer will be as far as getting something to the voters,” McNally said.

The proposal calls for a 0.7 percent sales tax collected for a 10-year period. About a third of the proceeds would go to transit projects, while two-thirds would go into the state’s Highway Users Tax Fund.

From there, 60 percent would head to the Colorado Department of Transportation, 22 percent to counties, and 18 percent to cities and towns.

CDOT would probably net about $243 million a year under the proposal, which would fill a sorely needed gap in transportation funding, said CDOT spokeswoman Amy Ford.

“We are short about $800 million” to pay for maintenance, rural road safety and congestion relief, she said.

CDOT’s $1.1 billion budget has not been helped by the federal gas tax, the largest single source of the Highway Users Tax Fund. The gas tax has been at 22 cents per gallon since 1991.

To compensate, CDOT changed how it budgets for projects. Under its program RAMP, which stands for Responsible Acceleration of Maintenance and Partnerships, CDOT currently funds multiyear projects based on a year of spending, rather than banking the full amount of a project before construction starts.

RAMP also emphasizes public-private partnerships that allow CDOT to get to projects more quickly than if the agency waited exclusively on public funding.

But proponents say CDOT’s current funding stream will flow only for so long. Many rural towns need money now to fix badly pitted roads and byways.

“This isn’t just about the metro area,” McNally said. “When you listen to people in smaller towns, they need shoulders on their roads just to be safe. That’s just as important as anything we want.”

McNally said towns and cities in Colorado have long lists of transportation projects that need addressing.

But whether voters will go for such an across-the-board sales-tax increase a year from now is a mystery.

“Roads are like water. You take it for granted you’ll have water when it comes out of your tap until it doesn’t,” she said. “You don’t even think about roads until you can’t get to the hospital or to a job because the roads give you a flat tire.

“But who knows what people will think a year from now?”

Monte Whaley: 720-929-0907 mwhaley@denverpost.com or twitter.com/montewhaley