Ballari Jn - Look around and enjoy the station. A sacred place where Mahatma Gandhi once spent 8 hours. - Vishwanath Joshi

BUFFER : A buffer is a part of the buffers-and-chain coupling system used on the railway systems of many countries, for attaching railway vehicles to one another.
Fitted at the ends of the vehicle frames, one at each corner, the buffers are projecting, shock-absorbing pads which, when vehicles are coupled, are brought into contact with those on the next vehicle. The draw chain used between each pair of vehicles includes a screw which is tightened after coupling to shorten the chain and keep the buffers pressed together. Such is known as a 'screw coupling'. Historically, coupling chains were no more than that, a short length of heavy chain (typically three links long) with no adjustment. These would result in a 'loose-coupled train'...
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in which the buffers of adjacent vehicles would only touch when the coupling chain was fully slack, such as when being pushed or going down hill.

Although the buffers in the very earliest days of railways were rigid (dumb buffers), they soon came to be spring-loaded, while those fitted to modern locomotives and rolling stock incorporate oleo-pneumatic shock absorbers.

BUFFER STOPS / DEAD END : Dead-end sidings are often fitted with buffer stops to prevent vehicles running off the end of the track. These may consist of a simple transverse beam fixed at buffer height but the buffer stops at passenger stations can be elaborate hydraulic installations capable of absorbing a considerable amount of energy.
Friction buffer stops are clamped 'loosely' to the rails, and when hit by a train that fails to stop correctly, move with the train for perhaps 30 m (98 ft) scraping the top of the rails, which absorbs considerable energy.

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 km - 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