Question

why trains are running in track?why train are not run in road

Answer 1

The real answer goes back a long way - in the early days of horse drawn wagons, they found that running the wheels along slabs of smooth stone with grooves cut in was a much smoother way to transport goods, damaged wagons less, and prevented the wagons from leaving the route. Bear in mind early roads were absolutely appalling with large ruts, holes, troughs, puddles and goodness knows what else. 
The natural progression from there was to using precast metal bars or 'rails' and to fit wagon wheels with a 'flange' so that the wheel could not fall off one side or the other. 
And that's the way things developed - rails were much smoother and have much less friction resistance to a steel wheel than a tarmac road does to rubber, so much heavier loads can be moved with less power.

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Answer 2

because its to big that it cant run in and cause there will very noise and there will acsident because of large size . if we park it in parking zone it will cross three road that is zic-zac so train run in track.