The key question for state highway planners has to be: “Where do we start?”

Much of the state’s 23,000 miles of roads are crumbling and require maintenance, while new improvements are needed to ease traffic bottlenecks and create opportunities for commerce.

Highway funds come from the federal government, but even with the five-year transportation bill that has received bipartisan support in Washington this week, there won’t be enough cash coming into Maine to do everything that needs to be done.

That’s why the Maine Department of Transportation has adopted a new approach to setting priorities: To make the money go further, limited federal highway fund dollars will go first to projects that have private sector and municipal partners.

While there are potential problems with that approach, we think the DOT is making the right decision. Anything that can make transportation programs move forward is worth some risk, especially as political stagnation at the federal level appears to be spreading into state government.

The new approach has been first applied in Waterville, where a new I-95 interchange at Trafton Road will be funded by a three-way partnership among the state, the city and a Rhode Island land-holding company that owns 923 acres nearby.

The costs of the $4.8 million project will be divided this way: Trafton Properties Inc. and the state will each pay $1.8 million. The federal Economic Development Administration has awarded a grant for nearly $1 million and the city will pay the rest.

This project has been on the drawing board for years, but it was never approved because there was not enough money in the budget. The city will expand its tax base and the landowner will get higher property values in exchange for its infrastructure investment. And the state will have money available for other projects.

There are legitimate concerns about this kind of system. Without proper protections, landowners could use political influence to push unnecessary infrastructure improvements that would benefit only them, sending public money into private pockets.

But as long as the process is transparent and the partnerships are formed over projects that the DOT might have funded on its own if it had the money, this should not be a problem. The involvement of a municipal partner could help steer the money to projects that really deserve to be built.

This week, Congress approved a five-year transportation bill, which will put $305 billion into the nation’s infrastructure. That sounds like a lot, but even the bill’s supporters will say that it is not nearly enough to meet the country’s needs.

The bill was financed with gimmicks and rosy revenue projections instead of an increase in the gas tax, which is the only reliable source of funding for fixing and improving the nation’s roads. At a time of low oil prices, it’s a serious mistake to miss this opportunity to invest in transportation infrastructure without putting a drag on the economy.

The federal government’s timid approach means the Maine DOT can’t stop looking for bargains. The department’s decision to work with private sector partners is a good way to get more projects built.