The Federal Railroad Administration does not currently set any limits on train lengths – and also doesn't regularly track train lengths or their associated risks. That has allowed freight railroad companies to occasionally operate trains up to 8 kilometres (5 miles) long.

In the United States, there is technically no federal law that strictly limits the maximum length of a freight train, but operational and infrastructure constraints usually cap them at around 12,000 to 15,000 feet (approx. 2.3 to 2.8 miles). However, with the rise of "Precision Scheduled Railroading" (PSR), it is increasingly common to see "mega-trains" reaching lengths of 20,000 feet (nearly 4 miles). The primary limiting factors are the length of "passing sidings" (the side tracks where one train pulls over to let another pass) and the strength of the couplers that hold the cars together. To manage these massive loads, railroads use "Distributed Power," where locomotives are placed at the front, middle, and end of the train to provide balanced pushing and pulling force. While these long trains are efficient for moving bulk goods like coal or grain, they have sparked significant debate in 2026 regarding public safety, as they can block railroad crossings for extended periods, potentially delaying emergency vehicles and causing local traffic congestion.