PHOENIX - A group of automobile hobbyists took the first steps Monday to quash the chance of Arizonans having to pay to drive on roads they already paid to build.

An initiative measure would constitutionally prohibit the conversion of any existing publicly funded or maintained road into any form of toll road. Most significantly, it would block efforts to take lanes now reserved for high-occupancy vehicles and open them to single drivers willing to pay for the chance to use them.

The issue is not just academic.

The Maricopa Association of Governments is paying for a study on whether to convert existing HOV lanes on Interstate 10 and other highways into toll lanes.

That would affect not just local residents. Anyone trying to drive into or through the Phoenix metro area, particularly at rush hour, would be faced with the choice: Stew in traffic or pay up.

Rates would be set on a "dynamic" basis: The higher the congestion on the road, the more per mile to use the toll lane.

Backers need 259,213 valid signatures by next July 3 to put the measure on the 2014 general election ballot.

Al Tracy, chairman of the No Toll Roads in AZ Committee, said there are about 400 car clubs in the state affiliated with the Arizona Automobile Hobbyist Council. Tracy, president of the council, said he believes members can be rallied to help gather the signatures.

Nothing in the measure would bar the state from charging tolls on new roads. That is one of the options being discussed for construction of new highways, including the proposed Interstate 11, which could stretch from south of Tucson to Las Vegas.

Tracy said he has no objections to the kind of public-private partnerships that might be needed for new roadways. But he said it makes no sense to try to raise money by charging people to use something that already exists.

That's also the position of the Arizona Trucking Association Organization President Anthony Bradley.

"We have a highway trust fund to build roads," he said. "And truckers pay a huge portion of that funding." Bradley said charging people to drive on those already constructed roads amounts to "double taxation."

But the truckers won't be providing funds for Tracy's initiative. Bradley said they prefer to spend their resources on ways to find more money to build new roads, including the possibility of new or higher taxes.

Eric Anderson, transportation director for MAG, acknowledges that Arizona motorists already paid for the roads that are there now. But Anderson said plans to build out the system - and, in particular, add lanes and capacity - have stalled because tax revenues haven't kept pace.

One problem is that state gas taxes, which have been 18 cents a gallon for two decades, are not growing as fast as the number of cars and trucks on the road due to improved fuel efficiency. The same goes for federal highway aid.

Anderson also said a half-cent sales tax approved by Maricopa County voters for freeway construction is bringing in 40 percent less now than was anticipated in 2003. Further, state lawmakers have siphoned off some gas-tax revenues each year to help offset the cost of keeping the Department of Public Safety on the road without using other tax dollars.

Anderson said toll lanes can raise a lot of money quickly.

He said one idea is to double the number of HOV lanes, using revenues from single drivers willing to pay the toll to cover the cost. Or the plan could simply add tolls to existing HOV lanes without widening the roadway.