The NTSB is launching a special federal investigation into Norfolk Southern

The National Transportation Safety Board said it will take a comprehensive look at the railroad’s safety culture and will send investigation teams to investigate five significant accidents involving Norfolk Southern since December 2021.

The agency also said it is urging the company to take immediate action to review and evaluate its safety practices.

Norfolk Southern did not respond to a request for comment. It announced plans Monday to improve the use of detectors along railroad tracks to detect overheated bearings and other problems in response to last month’s Ohio derailment.

According to the NTSB, the crew of the train that derailed on February 3 outside of eastern Palestine, Ohio, received a warning from one such detector but were unable to stop the train before more than three dozen cars veered off the tracks and caught fire .

Half of the town of about 5,000 people had to be evacuated for days as emergency crews intentionally burned toxic chemicals in some of the derailed cars to prevent an uncontrolled explosion, leaving residents with lingering health concerns. Government officials say tests have found no dangerous levels of chemicals in the air or water in the area.

Within the industry, Norfolk Southern has built a solid reputation over the years as a safe railroad company, said Christopher Barkan, director of the Rail Transportation and Engineering Center at the University of Illinois.

But after the derailment of East Palestine, the pressure on the railroad has increased.

Transport Secretary Pete Buttigieg in February urged the country’s rail freight companies to take immediate action to improve safety while regulators focused on strengthening safety regulations. Buttigieg said the department will hold the railroad accountable for any safety violations that contributed to the Feb. 3 crash.

President Joe Biden said on Twitter after the derailment that the previous pattern of railroads defying safety regulations needs to change and that Congress should support efforts to improve safety.

Although government data shows derailments have been declining in recent years, there were still 1,049 of them last year.

While most do not cause major problems, two of the five accidents the NTSB has been involved in in Norfolk Southern since late 2021 resulted in the deaths of two workers.

The latest came on Tuesday when a train and dump truck collided at a Cleveland steel mill, killing the train attendant as he was standing on the outside of a car, authorities said.