Since the beginning of last year, six states — Maryland, Massachusetts, Pennsylvania, Vermont, Virginia and Wyoming — and the District of Columbia have either increased the gas tax or changed the way it's collected, so that the state tax drivers pay at the pump automatically goes up either with inflation or the price of fuel, according to the Institute on Taxation and Economic Policy.

At least four other states are currently considering similar measures, USA TODAY reports. They are: New Hampshire, Utah, Washington and Iowa. Could your state be next?

Here's what's currently under way:

• New Hampshire. The state, which hasn't raised its gas tax since 1991, moved a step closer last week to increasing its gas tax from 18 cents a gallon to 22.2 cents. The state Senate's powerful Ways and Means Committee approved the tax hike 4-1. The bill's main sponsor, Sen. Jim Rausch, a Republican from Derry, said he was optimistic about the bill passing. Two Democrats and two Republicans voted for the increase; one Republican opposed it. Gov. Maggie Hassan, a Democrat, has said she will sign it if it reaches her desk.

• Utah last raised its gas tax in 1997. The Legislature is considering a bill that would adjust the gas tax so it would increase along with gas prices. The bill, by Sen. John Valentine, a Republican from Orem, would mean the state's 24.5-cents-a-gallon tax would go up as gas prices rise, but the tax would never fall below 24.5 cents a gallon and there is no ceiling. The measure passed the House Transportation Committee last week and goes to the full House.

• Washington. The state Legislature, which last raised its gas tax in 2008, is considering legislation by Republican state Sen. Curtis King to raise the 37.5-cents-a-gallon gas tax by 11.5 cents to finance road projects.

• Iowa. The 21-cents-a-gallon gas tax was last raised in 1989. An effort to raise the gas tax led by Rep. Josh Byrnes, a Republican from Osage, appears to be headed toward failure. Gov. Terry Branstad, a Republican, told the Sioux City Journal last week that he doubts a gas tax increase will advance in the Legislature this year.

All the efforts face tough political battles. States have been extremely reluctant to increase the amount they levy at the pump: 24 states haven't raised the gas tax in at least a decade, and 16 haven't done so in 20 years or more, according to the Institute on Taxation and Economic Policy.

Some states are trying to avoid protracted fights over hiking the gas tax by linking the gas tax to inflation or making it a percentage of the price paid per gallon. That way, it goes up automatically as inflation or gas prices go up.