The no-tax-hike pledge might sound like a good idea to taxpayers, but the reality isn’t necessarily all that great.

In South Carolina, for example, the pledge is a major impediment to a long-overdue increase in the state gas tax.

At 16 cents a gallon, the tax is one of the lowest in the nation, and hasn’t been increased in 25 years, despite a backlog of road and bridge maintenance of some $20 billion.

The state Department of Transportation has taken steps to increase the available funding for maintenance and repair projects, at the expense of new projects. But it’s not enough.

Meanwhile, roads and bridges continue to crumble. Eventually, they will cost far more to replace than to repair. And conditions that contribute to motoring hazards get a pass, year after year.

Apparently that’s OK with the many state legislators who have signed the no-tax pledge. And while there was a decline in their numbers with the recent election, it was not as significant as in Congress (see Doyle McManus’ column on our Commentary page).

Thirty-three tax-pledge S.C. House members were elected, one fewer than served in the last session. In the state Senate, there will be 11, three fewer than last session.

But their number remains strong in the Statehouse, and includes Gov. Nikki Haley. They can easily gum up the works.

That doesn’t bode well for an objective consideration of the gas tax, even though there’s is a clear case to increase it.

The tax functions as a user fee to provide good roads to those who use them, proportionate to that use.

And the gas tax allows for a major revenue infusion from out-of-state motorists who use our roads — no small matter in a state where tourism is one of the primary industries.

But when legislators already have committed their votes to a single-issue group, the opportunity for responsible action is in danger of being lost.

The problem is similar to that experienced during the years’ long debate over hiking the state’s cigarette tax. The case was compelling, and legislators finally raised the tax in 2010.

The pledge is sold as an expression of fiscal conservatism, but reality says it’s mainly a political gimmick.

Here’s what Lt. Gov. Glenn McConnell said about it: “To sign that pledge is to turn your vote over to another person.”

Mr. McConnell’s refusal to sign the no-tax pledge during his many years in the state Senate reflected a healthy independence of mind. No one would accuse Mr. McConnell of being a tax-and-spend liberal.

House Speaker Bobby Harrell, R-Charleston, similarly has refused to sign the pledge, and has cautioned newly elected House members to be wary of such commitments.

Legislators should be accountable to their constituents, not to a single-issue group with a simplistic view of public finance.

Failure to raise the gas tax would show how the pledge encourages legislators to act irresponsibly, even when the well-being of their constituents is at stake.