A unit train is a freight train carrying the same type of commodity, from origin to destination. Depending on the railroad and location, they can be between 65 cars in length and 200 cars (or more).

In 2026, the number of cars in a train depends heavily on the type of train and the country's infrastructure. For passenger trains, most consist of 8 to 12 cars (roughly 200–300 meters), though high-speed trains like the Eurostar or Japan’s Shinkansen can have up to 16 cars. In the U.S., Amtrak’s Northeast Regional typically runs with 6 to 9 cars. Freight trains are a different story, especially in North America. In 2026, "Precision Scheduled Railroading" (PSR) has pushed freight train lengths to extremes, with many trains averaging 150 to 200 cars, stretching over 2 miles (3.2 km) long. Some "super-trains" have even been tested with over 300 cars. However, this has led to significant controversy in 2026 regarding safety and blocked railroad crossings, leading to new federal proposals to cap train lengths at 7,500 feet (about 1.4 miles) to prevent mechanical failures and ensure that emergency vehicles can cross tracks without being delayed for 20 minutes by a single passing train.