Gov. Nikki Haley has a plan for highway funding that is long on promise and short on details. So far, the only known fact about the plan itself is that it won't include a tax hike.

And the road funding plan won't be announced until January, after the November election. Why not provide all the details now and have the highway issue become a meaningful part of the debate between Gov. Haley and her Democratic challenger, state Sen. Vincent Sheheen?

The state's road problems are widely acknowledged. South Carolina has an estimated shortfall of $30 billion in highway needs over the next 20 years. Despite its comparatively small size, South Carolina has one of the largest state-maintained road systems in the nation. And despite long-term efforts to get local government to take over some of that mileage, the state's responsibility hasn't much diminished.

Meanwhile, the state's gas tax is 16 cents a gallon, one of the lowest in the nation, and hasn't been increased since 1987.

So many legislators have signed the "no-tax pledge" that road advocates have been pitching a badly needed gas tax hike as a user fee increase. So far the hardheads in the Legislature haven't been willing to recognize the dire need for road and bridge improvements.

But the tax is a user fee, and has the added benefit of being supported by the many out-of-state tourists who visit South Carolina, and those who motor through on the interstate. Indeed, the out-of-state contribution has been estimated at a surprisingly hefty 30 percent of total gas tax revenues.

By passing up a gas tax increase, the state's leadership is passing up a good deal for road funding. It's a better deal than the $500 million bond issue for roads approved by legislators in 2013, which will be paid off with general tax revenues.

Critics of the gas tax contend that it can no longer be expected to fully carry the freight of road construction and maintenance. Nevertheless, it remains the most important source of state road funding for the S.C. Department of Transportation by a large margin. Increasing that source of revenue is the first step to a long-term, comprehensive program to upgrade highway and bridge maintenance, repair and construction.

Rep. Todd Rutherford, D-Columbia, came out with a road funding plan last week that would depend on state revenues from casino gambling. Though unlikely to be approved, Rep. Rutherford's plan has the value of being specific. Casino gambling isn't allowed in South Carolina, and the state's terrible experience with video poker some years back says that an expansion of legalized gambling isn't in the cards.

According to estimates, South Carolina needs about $1.5 billion more revenue each year over the next 20 years to make the necessary improvements to transportation infrastructure.

Last year, the Legislature approved a $500 million bond issue, plus one-time allocations of $40 million for secondary road improvements and $50 million for bridge repair. That's far short of what is needed on an annual basis. This year, the Legislature did nothing to improve the situation.

Critics of the road-funding system complain with justification that the State Infrastructure Bank gets funding for projects that aren't necessarily priorities. Designed as a financing instrument for the Ravenel Bridge and other major projects, the SIB has become a power to itself on state highway projects, and clearly needs to be reined in.

But calls for SIB reform, or further improvements to DOT governance, shouldn't obscure the general need for additional road funding. Or the fact that a gas tax increase is the best way for South Carolina to provide it.

If the governor has a better plan, we shouldn't have to wait until January to hear about it.