ELLICOTT CITY, Md. (WJZ)—- Autopsy results are released for the two young women killed in the train derailment in Howard County as investigators make significant progress.

Mike Hellgren is following new details in the investigation.

There are two fields for this investigation. At the scene, where they have been running test trains slowly at four miles an hour on a close watch and also in Washington, D.C. at an National Transportation Safety Board (NTSB) lab where the data recorder and video from the derailed train are being looked at as they work to determine the cause.

Video From CSX Test Run:

The first train since the deadly derailment rumbled through Ellicott City testing the tracks as NTSB investigators still search for the cause.

Early Tuesday morning, the massive train traveling to Baltimore went off the tracks near the narrow Main Street bridge. Twenty-one cars overturned, dumping coal into the parking lot and street below. The incident crushed cars in a nearby parking lot.

According to federal investigators, the three crew members on the train saw and heard nothing unusual before the derailment.

The emergency brakes applied automatically, but investigators say that’s possible it happened after the derailment was already in progress.

As WJZ has reported, crews are already inspecting the structural integrity of the Main Street bridge, all critical steps after the worst train incident in the long history of this town.

“I want to make sure that when the trains come through, the road bed, the track bed is secure so we can start removing the coal to make sure that once we take the coal away, the wall is not going to come down,” Bob Frances of the Department of Inspections said.

Officials allowed WJZ to get a closer look at some of the work now going on underneath the Main Street bridge.

The derailed train’s data recorder shows there was a broken air brake line triggered an emergency brake.

Several lawmakers have called on CSX to review safety policies. The company has had several major incidents in Maryland, including the 2001 Howard Street tunnel fire in Baltimore.

“I’ve talked to Congressman Cummings, I’ve talked to Senator Mikulski’s office as well, not only about the safety of this area but also making sure that all the issues are repaired,” Howard County Executive Ken Ulman said.

Police also released the cause of death of the two teenagers– Elizabeth Nass and Rose Mayr– who were killed at the derailment scene while sitting feet from the tracks: Compressional asphyxia because they were buried in coal. Both deaths were ruled accidents.

Nass and Mayr were on that train bridge with their backs to the side of the train as it passed a few feet behind them.

Federal investigators are looking into whether their presence played a role in the derailment, but experts say that’s unlikely.

The last moments of their lives were documented on Twitter.

Link: The Young Victims

The NTSB says its investigation will take time as they piece together tracks and look at maintenance records and mechanicals.

“We’re investigating this accident not just to determine what happened but also to determine why it happened,” Jim Southworth of the NTSB said.

Several more test runs are planned before the tracks reopen.

CSX wants the track open soon. So far, the test runs have been successful.

“That’s our job here in Howard County to continue to support the efforts that the NTSB and the CSX are doing. We understand the challenges, especially for our merchants and residents down here, the inconvenience here,” Ulman said.

Link: Ellicott City Impact

This derailment also disrupted some Verizon communications equipment. And there were environmental concerns about the impact of that coal going into the Patapsco River.

Ulman is meeting with other county officials to continue to get briefed on the situation.

Interview With Howard Co. Executive Ken Ulman:

Video From Sky Eye Chopper 13:

Links to Related Stories:

Howard County Investigates Track Safety After Fatal Train Derailment In Ellicott City
Investigators Reviewing Camera Footage & Event Recorders From Ellicott City Train Derailment
Ellicott City Businesses Take Financial Hit After CSX Train Derailment
CSX Train Derails In Historic Ellicott City, Killing 2 Young Women Tweeting Near Tracks

Stay with WJZ.COM for the latest on this developing story.