SEPTA will spend $100 million for a new, federally mandated train-control system designed to prevent the kind of collision that killed 25 people and injured more than 130 in Los Angeles in 2008.

The new system must be installed by Dec. 31, 2015, under current federal law. The system will be designed to automatically halt trains if engineers do not heed stop signals.

SEPTA officials said the cost would mean canceling or delaying many other transit projects in the Philadelphia region.

The SEPTA board awarded a $98.7 million contract Thursday for the "positive train-control" system to Ansaldo STS USA Inc., a Pittsburgh-based subsidiary of an Italian signal-manufacturing company. The board also awarded a separate $1.7 million contract for related right-of-way work to Independence Constructors Corp., of Douglassville.

Congress required positive train-control systems on all rail lines that carry passenger traffic after a commuter train collided head-on with a Union Pacific freight train in Los Angeles in September 2008, killing 25 people and injuring more than 130.

The National Transportation Safety Board, which had recommended the use of the collision-prevention technology since 1990, found that the accident occurred because the commuter train's engineer was text-messaging and failed to stop for a red signal.

Congress is considering extending the deadline for railroads to install the new systems because of the cost and time involved.

"It's recognized nationally as a very aggressive date to hit," said Jeffrey Knueppel, SEPTA's assistant general manager and chief engineer.

The financially strapped transit agency will spend much of its capital budget over the next three years to pay for the train-control system, said Luther Diggs, assistant general manager of operations.

"We won't have one bridge, or substation, or station until we get this paid for," Diggs said. "It just means we won't do a lot of other things."

Already, SEPTA has postponed several big-ticket projects, such as the $100 million renovation of the City Hall subway station, because of a lack of money.

SEPTA borrowed $427 million last year to pay for new Silverliner V railcars now rolling into service and a new "smart card" fare-payment system that will be installed over the next few years.

In other business, the SEPTA board reelected Pasquale "Pat" Deon Sr. of Bucks County as its chairman, and it chose Thomas E. Babcock of Delaware County as vice chairman.

Contact staff writer Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com.