Take a car, add an electric motor and some batteries. Build in a special gearbox which combines the output of the motor with that of an internal-combustion engine. Now all you need is a sophisticated electronic control system, and the result is a hybrid car like the Toyota Prius. It saves fuel, because when the driver brakes the car stores the lost kinetic energy in the battery, and when the driver hits the accelerator the electric motor kicks in, using that stored energy. But it took Toyota 13 years to convince customers that the Prius principle is the technology of the future.

Now, it seems, it has convinced builders of railway engines, too. Like carmakers, they are trying to combine internal-combustion engines and electric motors to save fuel. ‘Development is so advanced now, that we can use it, too,