Question: What are the factors (both technical and operational) that affect the average speed of passenger and goods trains?

Answer: A train runs a 100 km line at 50 kmph. If we neglect accelerating and decelerating time, we have time of the journey 2 hrs. But if the train must stop somewhere en route for to give way to another train (eg. on a single track line) , it must stop for 6 minutes (0.1 hrs). Then (again neglecting accelerating and decelerating time) we have real speed 100/2.1=47.62 kmph. Increasing the top...
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speed twice to 100 kmph changes the theoretical time to 1 hr and real time to 1.1 hrs so the real speed is 100/1.1 = 90.91 kmph - not twice as much.
In the real world we may have more stops, longer stops but also top speed not improved so much, some tracks that cannot be upgraded to high speeds (too steep slopes, too tight bends etc.). Then, much of the higher top speed is "eaten" by the remaining factors.

Answered by: Przemyslaw Kowalik from Lublin University of Technology

Source: Researchgate.net