While it is true that the typical European train is about 40 cars (or 40 platforms, in the case of intermodal), these trains also often operate at much higher speed or on steeper grades. There are some alpine main lines with grades between 2 and 3 per cent.

I have seen a 40-car Austrian coal train that had as much horsepower as a typical Powder River Basin 120 car coal train. In this case, the train had three high-horsepower electric locomotives -- each about 8-10,000 horsepower).

The trains need this much power to operate at speeds compatible with the dense passenger traffic.

Most modern European freight cars are now of the "ss" classification, meaning that they are rated for speeds up to 120 km/h (about 75 mph). Some older or special purpose cars are just rated as "s" (top speed 100 km/h or about 60 mph). There are also freight cars classified as "s(s)" , meaning they can operate at 120 km/h depending on some conditions, such as the load factor. For example a coal unit train that can run at 100 km/h loaded can return empty at a speed of 120 km/h.

-- Ernest