VIRGINIA LAWMAKERS have given Gov. Robert F. McDonnell’s bold transportation funding plan mixed reviews, affirming his own prediction that nearly everyone would find something objectionable in it. That shouldn’t mean it’s dead on arrival in the General Assembly. Just as it’s the prerogative of legislators to wrinkle their nose at the proposal, it’s also their responsibility to improve it.

To no one’s surprise, some in Mr. McDonnell’s own Republican Party (as well as anti-tax oracle Grover Norquist) have blanched at his idea to raise the state sales tax on all goods by 16 percent, in lieu of the current gas tax. Also to no one’s surprise, Democrats are sour on the governor’s idea of cannibalizing other budget priorities — education and health, for instance — to pay for more road construction. The governor’s measure, said Senate Minority Leader Richard L. Saslaw of Fairfax, “is so dead it’s unbelievable.”

Fine. So let’s hear a politically realistic Democratic counterproposal — one that blends higher taxes, as Democrats want, with shifting existing revenue to transportation, as Republicans insist.

Our main objection is that Mr. McDonnell’s blueprint delivers too little money too slowly. Virginia needs $1 billion more for transportation annually starting now. Realistically, the McDonnell plan would yield barely $600 million, and it wouldn’t even ramp up to that amount until 2018. In the meantime, maintaining existing roads is draining away transportation dollars so fast that the state will be unable to pay for new construction by 2017. That can’t be allowed to happen.

The good news is that the governor’s plan can be easily modified both to generate more money and to make more sense. Its most bizarre aspect is the complete elimination of the tax on gasoline, with its revenue being replaced with the sales tax hike. We understand the political appeal — voters might buy the whole package if they can save money at the pump. But it makes no sense to relieve those who use the roads, including out-of-state drivers, of the obligation to pay for them.

Why not retain a gas tax, as every state now does, but at a lower rate indexed to inflation? If, for instance, lawmakers left most of the governor’s proposal intact but halved the current tax of 17.5 cents per gallon instead of scrapping it, the overall package would lower prices at the pump but also yield close to $1 billion annually.

The governor’s plan is a constructive starting point; to his credit, that’s how he’s presented it. But a new funding system must also make sense. As it stands, it makes no sense to abandon the principle of making drivers pay for the roads they use. It makes no sense to penalize drivers of alternative-fuel vehicles with a $100 annual fee, as Mr. McDonnell proposes, while drivers of gas-powered cars pay no state tax at the pump.

Further, it makes no sense to argue, as the governor does, that the gas tax is a dying revenue source when lawmakers could easily revive it with an inflation index.

And it makes no sense to incur the wrath of anti-tax ideologues in return for so modest an infusion of revenue. If the governor is brave enough to challenge his party’s own orthodoxy, he should go big.