JEFFERSON CITY — The Missouri Senate voted to raise the state’s fuel tax Thursday to help the state Department of Transportation avoid a major reduction in state highway maintenance.

If passed, the proposal would increase the tax on gasoline by 1.5 cents per gallon and raise the tax on diesel fuel by 3 cents per gallon.

Supporters said it would raise about $50 million per year in additional revenue for state highways and bridges, far less than the nearly $500 million the state Department of Transportation said it needs to maintain the existing system.

However, the amount raised by the Senate plan is low enough that it does not trigger a constitutional requirement to submit the increase to Missouri voters. A similar plan was voted down last August.

The bill’s sponsor — Doug Libla, R-Poplar Bluff — questioned the ramifications of not getting more money for the transportation system.

“What are we really doing here? Are we going to make things even worse where people can’t get to work?” Libla said. “Are we going to have companies not wanting to come to Missouri or expand in Missouri because they can’t get their freight moved, they can’t get their employees to work? What about our school districts when we start having buses that can’t get across?”

As part of the Senate compromise to end a filibuster, the measure includes provisions by which some state highways could be operated and maintained by a private company. However, the Senate added a provision to require legislative approval before a private company could impose tolls or other fees to generate revenue.

Sen. Ed Emery, R-Lamar, opposed the bill. He suggested bringing the issue to a vote so that Missourians could decide for themselves whether or not they wanted an increased fuel tax.

“We could have sent it to the vote of the people saying I promise not to raise your taxes, but if you want to raise your taxes in the face of the deteriorating roads and bridges then you’re welcome to do that,” Emery said. “But we chose not to do that.”

A majority of Republicans in the Senate voted against the tax hike, but it passed with full support from Democrats.

The measure requires one more vote in the Senate before going to the House.

The House Transportation Committee defeated a similar gasoline tax increase earlier this month.