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CHICAGO — Illinois voters overwhelmingly supported amending the constitution to require all transportation taxes and fees be spent exclusively on transportation projects.

With nearly 40 percent of votes counted, the amendment had the support of 79 percent of votes cast. It needed 60 percent of the vote to become law.

The proposal overwhelmingly passed the state General Assembly earlier this year.

The amendment declares that all revenue raised for the stated purpose of funding transportation projects must end up directly funding transportation projects.

In the past, some revenue raised through methods like vehicle registration fees and excise taxes on gasoline were diverted to fund health care, education programs or social services.

This amendment not only bans those kinds of diversions — it makes them unconstitutional, along with any new laws or provisions that might allow for them. In other words, it creates an untouchable "lockbox" of funding to be used solely for transportation projects, hence the amendment's nickname.

This joins pension funding, in terms of protection in the Illinois constitution, potentially limiting funding for areas like health care, social services and school and university funding.

The measure was backed by groups like the Metropolitan Planning Council, which points to a sharp drop-off in funding for public infrastructure projects all over Illinois. The state's cratering transportation deficit will only get deeper if special measures aren't taken, it argues.

"We know from polls that a big reason people are opposed to raising gas taxes is that they don't have confidence the money would actually be used for transportation," said Jim Reilly, a senior fellow at the council. "A gas tax is a user fee, so we shouldn't be spending it elsewhere."

A broad coalition of business and transportation advocates around the state, including the Illinois Chamber of Commerce, the Illinois Construction Industry Council and the American Society of Civil Engineers, heavily backed the push for the amendment.

The Chicago-based Active Transportation Alliance also expressed cautious support for the measure, trusting that it would "significantly [increase] state funding available for walking, biking and transit" and not just roadways, according to a statement.

But others, like Amanda Kass, assistant director of the University of Chicago's Center for Municipal Finance, published a six-page paper cautioning voters against approving what she called a "highly problematic" amendment.

For one thing, she said, lawmakers trying to wade out of a severe budget crisis would be tying their own hands by restricting how they can use revenue.

"If you think of the entire revenue pie, all this would do is limit the ways that it can be sliced up," Kass said. "But it wouldn't add to the pie. The pie is already too small to begin with, so this would just deepen the hole."

Plus, she said, the vague wording around which "forms of transportation" can get direct funding could bring unintended consequences.

"It's not like a state statute that lawmakers would have the power to change on their own," Kass said. "A court would have to weigh in on everything, using the actual language of the amendment, and that alone should make voters cautious."

Here is the full text of the amendment:

"The proposed amendment provides that no monies derived from taxes, fees, excises, or license taxes, relating to registration, titles, operation, or use of vehicles or public highways, roads, streets, bridges, mass transit, intercity passenger rail, ports, or airports, or motor fuels, including bond proceeds, shall be expended for other than costs of administering laws related to vehicles and transportation, costs for construction, reconstruction, maintenance, repair, and betterment of public highways, roads, streets, bridges, mass transit, intercity passenger rail, ports, airports, or other forms of transportation, and other statutory highway purposes, including the State or local share to match federal aid highway funds."

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