An emotional Amtrak CEO pledged to lawmakers Tuesday that safety technology that could have prevented a deadly derailment last month in Philadelphia will be put into operation, while Democrats and Republicans exchanged barbs over whether Congress or the Obama administration is most to blame for railroads not installing the technology.

“We are responsible for the incident and its consequences,” Joseph Boardman told a House transportation committee hearing. His voice breaking, Boardman said equipping trains with positive train control, a technology that can prevent trains from derailing because of excessive speed, is the “single greatest contribution my generation of railroaders can make”.

Amtrak had already installed the technology on tracks it owns in the Northeast Corridor from Boston to Washington, but it wasn’t in operation when Amtrak Northeast Regional train 188 entered a curve in Philadelphia at 106 mph on 12 May. The speed limit for the curve is 50 mph. Eight people were killed and about 200 injured in the derailment.

Several lawmakers raised questions about the train cars involved in the derailment, which were severely mangled. The cars were purchased beginning in 1975 and weren’t built to modern occupant protection standards, Boardman said. They haven’t been replaced because the railroad is still trying to replace cars built in the 1940s, he said.

Accident investigators are looking at whether improved train cars could have prevented injuries or deaths in the Philadelphia crash, said Chris Hart, chairman of the National Transportation Safety Board.

Emergency personnel work at the scene of a deadly train wreck in Philadelphia on 13 May 2015. Photograph: Patrick Semansky/AP

At the start of the hearing, the NTSB released a preliminary report that says investigators still don’t know whether the engineer involved in the Philadelphia derailment was on his cellphone before the speeding train crashed. It also remains unclear whether damage to the windshield was caused by the wreck or an object thrown at the train, the report said.

The NTSB has said engineer Brandon Bostian, who suffered a head injury in the crash, has been cooperative but says he cannot recall the moments before the accident. The two-page preliminary report estimates damage from the crash at more than $9.2m.

Several Republicans, including Rep Jeff Denham, a Republican from California, told Hart that they were baffled that three weeks after the crash, accident investigators still could not say for certain whether Bostian was using the cellphone while the train was in operation.

The phone was used to make calls and send text messages the day of the accident, but inconsistencies in phone records were presenting difficulties, Hart said. The voice and text messages were recorded in different time zones and may not have been calibrated to the exact time used by other equipment on the train, such as a camera focused on the tracks and a recorder that registers how fast the train was moving and actions by the engineer, he said.

“We were surprised at the complexity of that ourselves, and we’re experts at this,” Hart said. “It’s very crucial to get that fact right. We will not be hurried into giving an answer.”

Congress mandated in 2008 that Amtrak, commuter railroads and freight railroads install positive train control by the end of this year. Amtrak still has to do extensive testing of the system, but will meet the deadline, Boardman said. Most other railroads will not. Only Burlington Northern-Santa Fe has submitted paperwork saying it has completed a positive train control system. At least two commuter railroads are also expected to meet the deadline.

Amtrak could have installed positive train control sooner if it had had more money from Congress years ago, when it first began work on the system, Boardman said. Amtrak’s positive train control system relies on transponders, while most other railroads are installing systems that use GPS and wireless technology. The systems automatically slow or stop trains if they are travelling too fast, are about to collide with another train, disobey signals or enter an area where crews are working.

Sarah Feinberg, the acting Federal Railroad Administration administrator, told the committee that the agency intends to enforce the 31 December deadline for all railroads to install positive train control. Last week, railroad administration officials told a special advisory committee that enforcement could include fines and even a shutdown of operations for railroads that don’t comply.

Obama administration officials have repeatedly asked Congress to give them the power to extend the deadline on a case-by-case basis for railroads that demonstrate a sincere effort to install the technology. However, legislation introduced by Senate Commerce, Science and Transportation Committee chairman John Thune, a Republican from South Dakota, and other members of the committee would grant railroads a blanket extension of another five to seven years.