Factbox: U.S. public-private partnerships in play

Across the United States, more state and local governments are tapping private dollars to build, repair and maintain public infrastructure. Here are some of the biggest and most-watched projects:

If the project were to use traditional public financing, it would cost about $1.2 billion, said Bryan Kendro, director of public-private partnerships in Pennsylvania's Transportation Department.

"We expect proposals to come in well below that," he said.

The Port Authority will reimburse the private developers with regular payments for making the road or bridge available for use. The use of these "availability payments" is on the rise, said John Medina, a global project analyst at Moody's Investors Service.

The same company is designing and building both bridges. Indiana helped the developer finance the project with nearly $677 million of tax-exempt private activity bonds in March 2013. The state will also make availability payments and milestone payments.

The state says the private sector is expected to invest $500 million to $900 million in the project, which has a total price tag of $2.2 billion. Construction could be completed by spring 2015.

The state hopes to have a contract signed by July, a spokeswoman said. The project, which is estimated to begin in winter 2015, will cost at least an estimated $2.8 billion and will rebuild 15 interchanges, replace more than 75 bridges, add four tolled express lanes and rebuild general use lanes.

(Editing by Dan Burns and Douglas Royalty)