For the first half of the year in Missouri, sales of fuel have been down compared to last year in every month but April. Sales of gasoline are up slightly but sales of diesel fuel are down dramatically, dragging down the total number of fuel gallons that have been sold.

That sagging trend line means a big decline in funding for the Missouri Department of Transportation -- and an even bigger headache for the politicians who will have to deal with it.

The consumption of fuel in Missouri, based on fuel tax receipts by the state, is down over last year for five out of the last six months, including a staggering 9 percent dip in May.

“The picture is not very pretty,” said Springfield Area Chamber of Commerce President Jim Anderson, the vice chairman of the Missouri Highways and Transportation Commission. “And that's a trend we're going to see continued.”

That means the state is losing the 17-cents-per-gallon fuel tax on millions of gallons of gasoline and diesel.

The fuel tax is used to fund new road construction projects, repairs and bond repayments on already completed projects. The consistent decline has left politicians scrambling for a new revenue source.

“I don't have a preference other than the gas tax increase will not raise sufficient revenue,” said U.S. Rep. Kenny Hulshof, a Republican candidate for governor, at a campaign forum.

All three major candidates for governor have ruled out raising the fuel tax but all have also shied away from specifics.

“None of them is zeroing in on a specific proposal which I think is the answer. In my mind, I don't think it will be one proposal. I think it's going to have to be two to four (proposals) to provide revenue necessary to make it work,” said Anderson.

One option is setting aside general revenue, money that would have to come from other state agencies and programs.

“I know there was a proposal to earmark 10 percent of general revenue; I think that's worth looking at,” said State Treasurer Sarah Steelman, a Republican candidate for governor, at a campaign forum.

Another idea is scrapping the fuel tax altogether and raising the state sales tax. That's something none of the candidates will go near.

“I know you are trying to push me into a corner,” Hulshof said in an interview with a reporter.

But the phrase the candidates all consider intriguing is “public/private partnerships.” An example is building parallel truck lanes along interstate 44 with private funds.

“When you talk about truck lanes, toll roads, all that stuff has to be on the table when you look at transportation, but I think you have to have some benchmarks to be careful,” said Attorney General Jay Nixon, the likely Democratic candidate for governor in November.

What they all can agree on is that it will be important for the next governor to build support from state leaders and voters for a plan that will solve the funding shortfall for transportation.