THE RULING Democratic triumvirate in Annapolis — Gov. Martin O’Malley, Senate President Thomas V. Mike Miller Jr. and House Speaker Michael E. Busch — has linked arms behind a transportation plan designed to keep Maryland in the road-building business beyond 2017, when it’s projected to run out of money for new projects. Now they will have to mount an effort to sell it.

In addition to reaching recalcitrant state lawmakers, the leaders’ pitch needs to target a skeptical public. Recent polls, including one conducted by The Post, have shown that Maryland residents have not made the connection between terrible traffic and the erosion of the state’s main source of transportation funding, the gasoline tax, which hasn’t been raised in 20 years.

Mr. O’Malley has proven himself adept at making the case for expanding gambling; legalizing same-sex marriage; subsidizing higher education for immigrant students; and raising taxes to balance the budget. The transportation bill may be his toughest sell yet and a stiff test of leadership. It would raise a variety of taxes and sensibly link transportation revenue to inflation, while potentially bumping up gas prices at the pump by 16 cents a gallon over the next couple of years.

It’s worth the trouble. Two years ago a blue-ribbon state commission recommended a combination of new taxes and fees that would yield $870 million in annual revenue. At the time, that was regarded as the minimum needed to maintain roads, rails and bridges and fund top-priority new projects.

The blueprint unveiled Monday by Mr. O’Malley and the legislature’s top two leaders is more modest. On a phased-in schedule, it would yield less than $700 million in new funding, or $833 million if you include the additional borrowing the legislation would enable. And it would reach that level only gradually, in 2018.

All told, the Maryland plan — not counting $1 billion in new borrowing — would produce about $2.4 billion in new funding for transportation over the next five years. It does not include special regional funding, which was judged too tough a sell.

By contrast, Virginia, whose funding deficit is roughly comparable, has just enacted legislation that, once fully implemented in 2018 and beyond, will yield about twice as much money annually as Maryland’s plan. And that would include more than $500 million annually in regional funds for Northern Virginia and Hampton Roads.

There is no denying that raising new money for transportation is a heavy lift in Maryland, which has already sustained two major tax increases in the past six years. Still, this is the time to do it. With gubernatorial and legislative elections on the ballot next year, any significant revenue-raising legislation will be off the table. That would push the question off until 2015, when traffic will be worse and the funding deficit dire.

To the credit of Messrs. O’Malley, Miller and Busch, they have chosen to fight to safeguard a critical component of Maryland’s future prosperity.