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The head of the influential Texas Senate Transportation Committee proposed Wednesday a constitutional amendment that would funnel part of the money generated by vehicle sales taxes to building and maintaining roads strained by a booming statewide population.

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Jacksonville Republican Sen. Robert Nichols said if car and truck sales stay strong, the plan could mean $2-plus billion annually for traffic-clogged roads, highways and bridges. It would also allow top Texas conservatives to keep campaign promises about bolstering transportation infrastructure without raising taxes or expanding toll roads.

“We’re not talking about creating a new tax, we’re talking about capturing a portion of the tax you pay on your car or pickup,” Nichols said at a Texas Capitol news conference, flanked by Lt. Gov. Dan Patrick, who heads the Texas Senate.

Taxes collected on vehicle sales currently flow into the state budget’s general revenue. If passed by the Legislature and approved by voters, Nichols’ plan wouldn’t touch the first $2.5 billion generated annually, but would divert the rest for transportation infrastructure beginning in the 2018-2019 state budgetary cycle.

Nichols said that cementing the change constitutionally was necessary so that the Texas Department of Transportation could budget long-term expenses, without worrying that future Legislatures would alter its funding.

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Voters have supported constitutional amendments approved during the 2013 legislative session each of the past two years.

They passed one in November 2014 tapping Texas’ Rainy Day Fund for more than $1 billion annually in transportation funding, and approved in November 2013 a $2 billion amendment for drought-fighting water infrastructure projects.

Still, transportation officials say they need at least $4 billion per year just to meet current demand.

Patrick noted that the Senate’s preliminary draft budget for 2016-2017 includes $600 million per year in extra transportation funding, but that Nichols proposal goes farther.

“Our economy depends on it,” he said “not just the time value that’s lost in traffic for families that are commuting, but for moving goods and services it’s very important.”

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