Question

why small gap left between two railway tracks

Answer 1

because of the small gaps left between the rails,when trains pass over jointed tracks they make a clickety clacksound unless it is well maintained jointed

Answer 2

each rail is connected to the to the other in such a way that they have gap between them .the small gaps provide space for easy expansion of the rail which happens during summer as well as due to continuous fiction between the train wheels and the rails .