Amtrak had installed the "Positive Train Control" system on the track where a speeding train fatally crashed Tuesday, but the system was not switched on.
The system could have automatically slowed the Amtrak 188, but instead it jumped the rails, killing 8 people and injuring more than 200.
According to a top congressional aide, Amtrak told the House Appropriations Committee on Thursday that the PTC system was installed along the section of track outside Philadelphia's 30th Street Station, where the crash occurred, but it was not operating.
The aide said Amtrak informed the committee it has encountered delays turning the PTC on throughout its system because of the need to get the bandwidths required to upgrade the radios to a higher MHz, which improves reliability.
Amtrak has worked out a deal with the Federal Communication Commission to get the broader bandwidth either late last year or early this year, an aide said.
It has spent $110 million on the PTC system over the past five years.
House appropriators are now trying to find out why the system wasn't turned on sooner.
Democrats and Republicans, meanwhile, are dueling over whether insufficient funding of Amtrak led to the crash.
House Speaker John Boehner, R-Ohio, said Thursday funding was not the issue, but rather the high speed at which it was being driven.
The train engineer approached the curve at 102 miles per hour, more than twice the speed limit.
But Democrats said funding could have prevented the crash by hastening the installation of the PTC.
"Speaker Boehner's comments are patently false," Chuck Schumer, of New York, who is the No. 3 Senate Democrat, said.
"Experts have made clear that Positive Train Control could have prevented the tragedy in Philadelphia," Schumer said. "It is simply a fact that insufficient funding for Amtrak has delayed the installation of PTC, and to deny a connection between the accident and underfunding Amtrak is to deny reality."
Republicans point out they funded fiscal 2016 rail safety programs at 2015 levels and made no cuts. They slashed about $200 million from the rail infrastructure budget.
According to the Association of American railroads, installing PTC will cost about $9 billion by the time it is fully implemented.
The association calls for moving the deadline to finish it past the December 2015, but not for lack of funding.
"Due to PTC's complexity and the enormity of the implementation task," the an association statement said, "and the fact that much of the technology PTC requires simply did not exist when the PTC mandate was passed and has had to be developed from scratch, much work remains to be done. Despite railroads' best efforts, various technical and non-technical challenges make full development and deployment of PTC by 2015 impossible."