The Norfolk Southern freight train transporting toxic chemicals when it derailed in East Palestine, Ohio, earlier this month had already broken down once on its route — as workers express concerns about the train’s size.

The train broke down at least once between when it departed from Madison, Illinois, on Feb. 1 and when it derailed on Feb. 3, employees familiar with the matter told CBS News.

Employees say the train’s massive length and weight likely contributed to its initial breakdown and derailment.

The train totaled 151 cars — equating to about 9,300 feet in length — and weighed 18,000 tons, which is much larger than employees said was safe.

“We shouldn’t be running trains that are 150 car lengths long,” one employee told CBS, adding that they felt there should be limits on the weight and length of the trains.

“In this case, had the train not been 18,000 tons, it’s likely the effects of the derailment would have been mitigated,” the employee said.

Norfolk Southern CEO Alan Shaw declined an interview with CBS, but a company spokesperson said “the weight distribution of this train was uniform throughout.”

Still, the train was considered “very long,” according to Sarah Feinberg, who was administrator of the Federal Railroad Administration from 2015 to 2017.

“When I was FRA administrator, I was not happy with the lengths of the trains, and they were 80 or 90 cars long,” Feinberg said. “This train was 50 percent longer.”

While more efficient for railroad companies, the longer trains pose greater challenges for railroad crews, who are already overworked and exhausted, an employee told the outlet.

The initial derailment caused a massive fire, releasing large clouds of black smoke. The train was carrying hazardous materials including vinyl chloride, butyl acrylate, ethylhexyl acrylate and ethylene glycol monobutyl ether.

The main chemical burned was vinyl chloride, an ingredient used to produce plastics and PVC, which has been shown to cause cancer at high levels of exposure.

The incident forced hundreds of residents to be evacuated from the vicinity of the crash so that authorities could conduct a controlled burn of the train cars’ chemicals in order to prevent an explosion.

After running tests on the air and water, local authorities last week gave residents the green light to return to their homes — but many residents remain skeptical, some citing a burning sensation in their eyes, animals falling sick and a strong chemical odor looming over the town.

The National Transportation Safety Board is investigating the derailment.

In a statement Tuesday, the agency said it had “identified and examined the rail car that initiated the derailment,” and said surveillance video “showed what appears to be a wheel bearing in the final stage of overheat failure moments before the derailment.”