Amid the gleaming, freshly painted diesel locomotives in the test shop of General Electric’s Erie, Pennsylvania, locomotive plant, it can be hard to spot the workers. They spend most of the time inside the vehicles using laptop computers plugged into the locomotives’ electronics to check for faults. The reliance on computer testing underlines how, while the newest of North America’s tens of thousands of freight diesel locomotives outwardly resemble their decades-old predecessors, the technology inside has been transformed.

Engines, motors and control systems have all been modernised as GE and Electro-Motive Diesel (EMD), the two companies that share a duopoly, compete to meet railroads’ demands.