The Utah Transit Authority announced Thursday that it gave the greenlight to Siemens Transportation Systems Inc. of Sacramento to begin building 77 new TRAX light-rail cars at a cost of $277 million. The new S70 rail cars are destined to ply some of the 70 miles of new track the agency is laying as part of its Frontlines 2015 project.

The cars will be delivered over four years on a schedule to coincide with the completion of new TRAX lines along the Wasatch Front. UTA general manager John Inglish said the new rail service will provide some relief from the pains of rapid population growth.

"Utah is the fifth-fastest growing state in the U.S. and the expansion of our rail system brings us closer to creating a more sustainable and less congested metro area for us and the next generation," Inglish said.

The first of the five new lines that comprise UTA's Frontlines 2015 plans — a 10.5 mile TRAX branch that runs through West Jordan off the current Salt Lake City-Sandy route — broke ground Thursday and will be followed by other TRAX extensions in Draper, West Valley City and to Salt Lake City International Airport. New commuter rail is part of the plans as well, with FrontRunner South scheduled to connect Salt Lake City to Provo.

The UTA rail vehicle contract is the biggest of its kind for the U.S. subsidiary of the German company, Siemens AG.