There is a small gap between two rail lines so that no 2 trees get touch with each other , if there is a fault then there is a  way for the mechanic and if the train stuck the passengers may get down easily.      
These gaps which are of the order of a few millimeters are provided to allow room to rails to expand the rise in temperature due to atmosphiric temperature as well as the friction caused by running of the train.all materials expand when heated and contract when cooled. since each section of the rail is very long the expansion due to heating is significant and unless space is provided for expansion of rails the rails will bend to accomodate the increased length

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