DAYTON, Ohio — On the road in a tour bus this week, the U.S. transportation secretary is spreading some bad news: the government’s Highway Trust Fund is nearly broke. If allowed to run dry, that could set back or shut down projects across the country, force widespread layoffs of construction workers and delay needed repairs and improvements.

Anthony Foxx kicked off an eight-state bus trip in Ohio to whip up public support for congressional approval of legislation to keep federal transportation aid flowing to states for another four years, and possibly longer. But Congress will have to act fast. The trust fund – the source of much of the aid – is forecast to essentially run dry sometime before the end of the federal fiscal year Sept. 30, and possibly as early as late August.

If that happens, the government will have to slow down or even halt payments to states, which rely on federal aid for most major highway projects. Uncertainty over whether there will be enough funds in the coming months is already causing officials in states like Arkansas, California and Colorado to consider delaying planned projects.

Foxx’s warnings this week echo ones by President Obama, who cautioned in February that unless Congress finished a bill by summer’s end then “we could see construction projects stop in their tracks.” But there is little interest among politicians in an election year to consider raising gasoline taxes.

Many transportation insiders, including Foxx’s predecessor, Ray LaHood, predict Congress will wind up doing what it has done repeatedly over the past five years – dip into the general treasury for enough money for to keep programs going a few weeks or a few months, at which point the exercise will have to be repeated all over again.

But keeping highway and transit aid constantly teetering on the edge of insolvency discourages state and local officials from moving ahead with bigger and more important projects that take many years to build. In 2012, Congress finally pieced together a series of one-time tax changes and spending cuts to programs unrelated to transportation in order to keep the trust fund solvent for about two years. Now, the money is nearly gone.

“Tell Congress we can’t slap a Band-Aid on our transportation system any longer,” Foxx urged state and local officials at a stop Monday to view one of Ohio’s biggest construction projects. Other states on the tour are Kentucky, Georgia, Tennessee, Alabama, Louisiana, Mississippi and Texas.

Foxx is promoting Obama’s four-year, $302 billion plan to shore up the trust fund with savings from proposed changes to corporate tax laws.