Human error wasn't the only possible cause of Tuesday's deadly Amtrak crash.
After decades of underinvestment, U.S. passenger rail systems are operating on an outmoded infrastructure that has been starved of the capital needed to maintain it properly.
"It's not just a matter of the human mistake in this case," said Robert Puentes, a senior fellow with the Brookings Institution's Metropolitan Policy Program. "We're not treating the system with the same kind of attention that we give to the auto sector, for example, where we have all kinds of safety measures."
The Amtrak crash, which killed eight people and injured more than 200, happened on a tight curve in Philadelphia where speeds were restricted to 50 miles per hour to prevent derailment. National Transportation Safety Board investigators have determined the train was traveling at more than 100 mph, though it has not concluded that speed alone was the cause.
The train might not have crashed if the stretch of rail had a speed control system Congress has mandated by the end of this year, NTSB member Robert Sumwalt said Wednesday.
That system, known as positive train control, is a series of devices that stop or slow trains to avoid accidents. Mandated by Congress in 2008, the system is required for all tracks that carry passengers or hazardous materials by the end of this year.
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But a bipartisan coalition in Congress has moved to delay implementation on behalf of industry lobbyists who say the timetable is too short and the system's costs have created an unreasonable financial burden.
Two more trains slipped off the tracks Thursday. Parts of a freight train derailed in Pittsburgh on Thursday morning, leaving some cars overturned or detached from their wheels. No injuries were reported. A train crashed into a semi in South Carolina that got stuck on the tracks, also without reports of injuries.
Privately owned freight railroads have invested hundreds of billions of dollars to upgrade tracks and other infrastructure over the past decade, according to the American Society of Civil Engineers. Between 2000 and 2011, the total came to more than $450 billion.
That compares with federal investment in Amtrak of about $30 billion over the period, according to the report. The result is a maintenance backlog of $6 billion on just the Northeast Corridor alone. The list of crumbling infrastructure includes more than 200 bridges, most dating to the turn of the 19th century, rail junctions and crossovers that are "functionally obsolete" and electric traction systems on 1930s-era components, according to a five-year financial plan published in 2013.