The 65-mile freeway project, which hasn't yet been funded and has no start date, would take three or four years to complete.

UTA, which hopes to build permanent commuter rail in Utah County if voters there approve a sales tax increase to pay for it, would be willing to invest $93 million in the temporary train because platforms and other infrastructure could also serve commuter rail should it be built, said agency spokesman Justin Jones.

The trains would run only during morning and evening commute hours, and would cost about $2 million to operate. But first, commuter rail would have to be identified as a preferred alternative in the transit portion of environmental studies of the proposed I-15 reconstruction that are scheduled to be ready within three years. If that happens, UTA could rent U.P. track during the three or four years the I-15 project will take to complete.

"When we did [previous] I-15 construction, people in Salt Lake had [travel] alternatives," Jones said. But if I-15 is out of commission in Utah County, congestion would become impossible, he said.

"There are no north-south alternatives," Jones said. "It becomes a major issue we begin planning for now. We just cannot shut down I-15 in Utah County for four years."

The Mountainland Association of Governments and Utah County officials first heard the proposal about a month ago. The goal is to make commuter rail, now known as Front- Runner, a permanent addition to the Mountainland long-term master plan. Once funding were secured, UTA would build its own tracks parallel to the U.P. line, Jones said.

- Patty Henetz