Unofficial returns for Proposition 104 show 55 percent of voters supporting the initiative with 45 percent voting against it.

The city's 0.4 percent sales tax for transit will increase to 0.7 percent for transportation, beginning Jan. 1 and lasting 35 years. The sales tax is the foundation of a $31.5 billion plan that will be funded by a variety of sources including federal grants and fares.

About 35,000 votes have yet to be counted, or about 26 percent of the total ballots cast. Another update won't come until Friday, according to the City Clerk Department.

The success of Prop. 104 is a victory for Phoenix leaders promoting the tax since the City Council approved the measure in March. Mayor Greg Stanton, who formed a citizens committee last year to envision Phoenix's transportation future, spent much of the summer campaigning for the measure over his own bid for reelection.

Supporters of MovePHX, the campaign in favor of the plan, crowded DeSoto Central Market to watch early results. They joined Stanton's election night party at the downtown spot near the light rail.

Stanton claimed victory for Prop. 104 after early results were released, calling the infrastructure investment a historic moment for Phoenix.

"This is a great night for the future of the city of Phoenix," Stanton said.