Joints in train tracks are designed with extra space to allow for what?
All metals expand when heated. The expansion of each metal is a function of its thermal properties and vary from metal to metal. When laying down railway tracks, sufficient spacing is allowed between two successive rails to allow for expansion of tracks during summer months. This spacing causes slight discomfort during the travel, since the train motion is not very smooth and this also causes noise. Yet, this spacing between joints is necessary to allow for expansion and contraction of the track material. Imagine what will happen, if there were no spacing between successive tracks. During the warm months, when the temperature is high, the track material will expand due to heat and the tracks will push against each other. During the night time, the tracks will contract and pull away from each other. The constant tug between the tracks will cause very high wear and tear and make the train motion unsafe.
Hope this helps.