JEFFERSON CITY, Mo. -- A state senator promoted a new plan Thursday that would boost money for highways without raising taxes by tapping into the natural growth of state revenue.

The proposal by Sen. John Loudon would direct 10 percent of the growth in state revenue toward highways, bridges and other kinds of transportation.

For the next fiscal year, Loudon estimates that could be $36 million. Because his proposed constitutional amendment would use 2008 as its base year, Loudon said it could direct more than $200 million to transportation by 2014.

"We're going to spur economic development by improving roads without a tax increase," said Loudon, R-Chesterfield.

If lawmakers approve it, the proposal would appear on Missouri's November ballot.

The idea drew praise from the chief engineer for the Missouri Department of Transportation, which has warned that a bonding-induced spike in highway spending is about to end. By 2010, Missouri's current $1.2 billion road construction program is expected to drop to $569 million. That's slightly less than the level before voters approved a 2004 constitutional amendment for new highway bonds and directing more existing tax revenue to the department.

Chief engineer Kevin Keith called Loudon's plan "an innovative suggestion" while stressing the department supports any solution to the impending transportation funding problem.

"Could this alone be the sole answer to all the transportation needs in Missouri? No, probably not," Keith said. "But could it be a major component of a solution? It could."

Missouri roads currently are financed predominantly through user fees such as federal and state fuel taxes, vehicle licenses and vehicles sales taxes. Dedicating a significant portion of general tax revenues to roads would mark a change in direction and would mean that money would not be available for such things as public education, prisons and mental health services.

But transportation officials said spending additional money on highways would create or sustain jobs, which in turn would generate more taxes for the state. Bonds could be issued against the expected future revenues from the measure, allowing more construction work to occur sooner, Keith said.

Both Keith and Senate Transportation Committee chairman Bill Stouffer stood alongside Loudon at a Capitol news conference as he outlined his plan with large, color charts displaying the mountainlike growth of money that he believes it would generate for transportation.

Stouffer, R-Napton, last year proposed a 1-cent sales tax, generating $7.2 billion over 10 years, to rebuild Interstate 70 and Interstate 44 with four lanes in each direction, two each for big trucks and other vehicles.

House Transportation Committee chairman Neal St. Onge, R-Ballwin, last year proposed to raise $4.1 billion over six years through a one-half cent sales tax plus a variety of higher fuel taxes and vehicle license fees. His plan would rebuild Interstate 70 with separate truck and vehicle lanes in each direction while also directing more money to other roads and modes of transportation.

Stouffer said Thursday that those proposed tax increases are unlikely to make it to the ballot this year. Because Loudon's transportation proposal contains no tax increase, it could be easier to sell to voters this year, Stouffer said.

Transportation plan is SJR43.