While the aftermath of a toxic train derailment in Ohio, U.S. two weeks ago is still in the air, the perils of the country's freight rail system has been brought under the spotlight as two Republican senators probed into it on Wednesday.

The derailment of a 150-car freight train on February 3 caused a fire that sent a cloud of smoke over the town of East Palestine in Ohio, forced thousands of residents to evacuate while railroad crews drained and burned off toxic chemicals. 

Though no fatalities or injuries were reported, residents complained about headaches and questioned the impact of pollution since the accident happened. 

They were told to return home on February 8 and were assured by environmental officials on February 16 that after being tested, the air and water close to the accident site had no contamination.

Perils of efficiency

The immediate cause of the derailment, according to the National Transportation Safety Board's preliminary investigation, was a wheel bearing on one of the train's cars overheating and failing just before the crash.

Two Republican senators, Marco Rubio and J.D. Vance sent a letter to U.S. Transportation Secretary Pete Buttigieg on Wednesday about railroad safety, saying "it is not unreasonable to ask whether a crew of two rail workers, plus one trainee, is able to effectively monitor 150 cars."

Such low-labour operation is widely welcomed by rail carriers by adopting the precision scheduled railroading (PSR) model to cut cost. Under PSR, trains are generally longer, overseen by fewer workers, and run on fixed schedules which leaves little or no time to conduct inspections. 

According to U.S. Government Accountability Office, six of the seven largest U.S. freight railroads have reported implementing PSR.

The rail union members believe that rail derailments have increased in recent years. 

Scrapped train brake system

Existing rail brake technologies in the U.S. on most trains date back to the Civil War era in some places, according to a report by The Independent in the U.K. 

In 2015, the Obama administration had passed a rule that required trains carrying hazardous materials to adopt Electronically Controlled Pneumatic brakes which offer improved performance and provide better train control as all the cars receive the brake command at the same time.

The Trump administration, however, scrapped the regulation lobbied by rail carriers including Norfolk Southern, the company which operated the train that derailed in Ohio.

The Department of Transportation (USDOT) did not immediately comment to Republican senators' question, but Buttigieg addressed the criticism in a series of tweets.

Senator Ted Cruz, the ranking Republican on the Senate Commerce Committee, tweeted on Wednesday that he agreed with Democratic Representative Ilhan Omar that they needed a congressional inquiry and direct action from Buttigieg.

Buttigieg responded to Cruz on Twitter that "we could start by discussing immediate steps Congress could take to address rail safety & reduce constraints on USDOT in this area. Give us a call, we can do some good work."

There are on average 1,700 train derailments annually in the U.S., according to the U.S. Bureau of Transportation Statistics, a branch of the USDOT.

(With input from Reuters)