WASHINGTON A bill was introduced in the U.S. Senate last month that would peal back the tax benefits private companies get from leasing public highways, making those privatization deals less attractive to investors.

Sen. Jeff Bingaman, D-N.M., chairman of the Senate Finance Committees panel that oversees infrastructure issues, and Sen. Chuck Grassley, R-Iowa, the finance committees top-ranking Republican, co-sponsored the bill.

The Bingaman-Grassley measure would stretch out the depreciation and amortization periods for highway investments.

Bingaman introduced a second bill that would deduct privatized highway miles from a states mileage total used to calculate federal aid for roads and bridges, a move that would cut into a states share of federal highway money.

In introducing the bills, Bingaman said states "should have some latitude to determine how to operate their own highways, [but] that doesnt mean that the federal taxpayer should subsidize selling off these highways."

Bingaman said his subcommittee "uncovered ... [that] the federal government - and taxpayers in all states - now subsidize these deals through exceedingly generous tax provisions."

A spokesman for Bingaman said the goal is to make sure that taxpayers are treated fairly when it comes to the privatization of highways.

Federal tax law now allows companies that lease highways to depreciate the value of the lease over 15 years, while the actual length of highway leases and proposals tend to be much longer. Indiana, for example, has leased its toll road for 75 years.

Also, concessionaires can amortize, or recover the costs, for the intangible benefit of the right to collect tolls over 15 years, while receiving that benefit over the full length of the lease.

"Were subsidizing these transactions in a way thats just not fair," added the Bingaman spokesman.

The tax bill would change the tax code to allow companies leasing a highway or a bridge or other piece of infrastructure to depreciate the cost over 45 years, the estimated useful life of highways and streets.

The bill also would push out the amortization period to 15 years or the length of the lease, whichever is longer.

The bill "takes the thumb off the scales so that these deals will either go or not go on their own merits but not because of tax advantages," said Tim Lynch, a senior vice president of American Trucking Associations.

Privatizing highways is a trend that began in 2004 with Chicagos 99-year lease of its Skyway for $1.8 billion to a Spanish-Australian conglomerate headed by the Macquarie Infrastructure Group.

The same conglomerate, which includes Spanish bank Cintra, paid $3.8 billion for its 75-year lease of the Indiana Toll Road.

Lynch and other critics argue that those deals - and others proposed or discussed in Pennsylvania, New Jersey and Massachusetts - are helped greatly by the tax provisions allowing quick repayment of costs.

"These are supposed to be privatized deals where the private sector can do something better than the public sector, but if you are skewing the deals because of tax benefits then maybe theyre not such great deals after all," he said.

The Obama administration has touted public-private partnerships as a way to help fund infrastructure improvements - without increasing fuel taxes, which Transportation Secretary Ray LaHood opposes.