UPDATED APRIL 6, 2016, 2:30 p.m.: Amtrak Train 89, the New York City-Savannah, Ga., Palmetto, partially derailed at Chester, Pa., approximately 15 miles southwest of Philadelphia, on the Northeast Corridor early Sunday, April 3, 2016, after striking a maintenance-of-way backhoe on the tracks. Two Amtrak maintenance-of-way employees were killed and 35 on board the train were injured, one seriously.

Amtrak Train 89 had 341 passengers and seven crew members on board at the time. Killed were the equipment operator and a track supervisor. Debris from the crash flew into the first two cars, injuring passengers. The train was traveling at 106 mph, 4 mph below its maximum authorized speed of 110 mph.

Amtrak suspended service along the Northeast Corridor between New York and Philadelphia, and SEPTA (Southeastern Pennsylvania Transportation Authority) also briefly halted service. Operations returned to normal by evening.

This was the second Amtrak wreck involving fatalities in the space of about a year. On May 12, 2015, the derailment of New York-bound Amtrak Train 188 at Frankford Curve in Philadelphia left eight people dead and more than 200 injured. Train 188 derailed due to an overspeed condition on a curve at which there was no civil speed restriction enforcement in place at the time.

Amtrak completed installation of ACSES (Advanced Civil Speed Enforcement System, its form of Positive Train Control), on the Northeast Corridor late last year. PTC systems are required to prevent incursions into established work zone limits without first receiving appropriate authority and verification from the dispatcher or roadway worker in charge. If employees establish a work zone on a particular track, it requires protection. If they do not establish a work zone, or report that they are clear of the track, releasing their authority back to the dispatcher, PTC cannot provide any protection. Does this latest accident indicate that ACSES—indeed, no PTC system—is 100% fool-proof and fail-safe?

“Just like any other engineering system, PTC only works when used properly, meaning it is still necessary for a track gang to formally establish a work zone,” observes one veteran railway engineering professional.

A veteran signal engineer writes:

“PTC is not the magic weapon that will end all accidents forever, as there is always something wrong with everything—even PTC. The devil is always in the details.

“The normal procedure in the NEC is to block the exit at the last interlocking before reaching the worksite in each direction. The current signal practice on the NEC has been to always provide a vital exit block on every main track leaving each interlocking with control from the dispatcher’s office, and a positive indication back on the dispatcher’s display showing which track is blocked. The signal system then positively prevents any signal from displaying an aspect more permissive than “Stop Signal” for any route leading to that exit. ACSES then enforces “PTS” (Positive Train Stop) at all “Stop Signals”—thus preventing any train from entering the out-of-service track between the adjacent interlockings. “The normal procedure in the NEC is to block the exit at the last interlocking before reaching the worksite in each direction. The current signal practice on the NEC has been to always provide a vital exit block on every main track leaving each interlocking with control from the dispatcher’s office, and a positive indication back on the dispatcher’s display showing which track is blocked. The signal system then positively prevents any signal from displaying an aspect more permissive than “Stop Signal” for any route leading to that exit. ACSES then enforces “PTS” (Positive Train Stop) at all “Stop Signals”—thus preventing any train from entering the out-of-service track between the adjacent interlockings.