The U.S. Federal Railroad Administration (FRA) is calling for a reevaluation of “train makeup” April 6, in the aftermath of a series of derailments. 

According to The Hill, the FRA issued a safety advisory, raising concerns about the makeup of trains and seeking to make sure that railroads “exercise due diligence” and are proactive in addressing possible safety risks in the way they build trains. The advisory states that the agency has observed an increasing trend in both build and makeup being potential causes or contributing factors in derailments. 

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The FRA said an analysis revealed several common themes among recent crashes, including that each one had 125 cars or more, all had much more than the maximum allowed 4,000 trailing tons and an empty car was the first to derail in all cases. Five out of six reviewed also had mixed freight trains, which usually require a more complex train makeup, and had hazmat cars, increasing the potential risks associated with a derailment. 

The analysis led the FRA to make six safety recommendations for railroads.