On roads, you must have observed that the roads are tilted inwards at turning points. This is done so that the necessary centripetal (centre-seeking) force is developed to prevent a vehicle from "moving out" or "losing balance" while negotiating a turn.
This type of "banking" is done in Railways as well.
Another reason why "banking" is done is to improve the balancing speeds at curves/turns. More the tilt, greater the balancing speed