The state’s cash-strapped Department of Transportation would get an extra $100 million a year in dedicated revenue under a plan recommended by House Speaker Bobby Harrell. The funding would help, but it’s still a half measure. Or less.

Rep. Harrell, R-Charleston, would shift the state tax collected on motor vehicle sales to the DOT. He reasons that auto-related taxes should go toward maintaining and building state roads.

That logic is sound, and if applied to the main source of highway funding the state gasoline tax, would require an increase that has long been needed to improve the state’s roads and bridges.

South Carolina’s gas tax is one of the lowest in the nation, at 16 cents, and hasn’t been raised since 1987. It legitimately serves as a user fee for motorists and has the added benefit of being supported by out-of-state motorists.

Indeed, a recent study done for the state Department of Transportation concluded that out-of-state motorists and truckers pay as much as 40 percent of the gas tax in South Carolina. That finding should make an increase in the gas a comparatively easy sell.

But legislators haven’t been willing to take a serious look at raising the gas tax for more than a generation. The only conclusion that can be drawn is that lawmakers aren’t willing to take the heat for raising taxes — even an essential tax related to road safety.

Gov. Nikki Haley also has proposed to put an additional $100 million into the highway fund, mostly from new revenues expected in the state’s general fund. Heralded as a funding solution for state roads, it badly underestimates the state’s road funding needs.

That figure has been estimated at $29 billion over the next 20 years. So together, the respective proposals from the governor and the speaker would generate a fraction of what is needed. In dollars, the sum is not to be dismissed. But, again, it’s not nearly enough.

Of course, Rep. Harrell’s plan could provide a lot more if the Legislature were willing to lift the outdated $300 cap on the vehicle sales tax. But previous suggestions about eliminating or at least upgrading the cap have been treated as if radioactive by legislators. Eventually, though, the Legislature is going to have to make some hard decisions on DOT funding if it hopes to finally bring the highway system up to speed.

Both the Harrell and Haley proposals would have the benefit of providing some new funding, as well as broadening revenue sources for the DOT.

But the state gas tax has served as the mainstay of funding for the department over the years.

To provide the DOT with the support required to meet priority road and bridge projects, the Legislature eventually will have to increase it.