I read that trains in pratice instead of acceleration to a certain speed level and holding the speed, they accelerate and then cost, accelerate again, und keep this pattern. This was shown by experiments. What is the explanation why this way of driving is more energy-efficient?
Just keeping a train at a fixed speed over level terrain takes a small fraction of the engine's power output. As a result, the engine runs very inefficiently.
In pulse and glide, the short bursts from the engine during the pulse phase are much higher power. These allow the engine to run at higher efficiency.
Roughly the same overall average power is produced by the engine either way, but with pulse and glide, that power is produced at a more efficient operating point of the engine.