Answer the following Q with stream of consciousness. Passage: A standard-gauge railway is a railway with a track gauge of 1,435 mm (4 ft 8 in). The standard gauge is also called Stephenson gauge after George Stephenson, International gauge, UIC gauge, uniform gauge, normal gauge and European gauge in the EU and Russia. It is the most widely used railway track gauge across the world with approximately 55 % of the lines in the world using it. All high-speed rail lines, except those in Russia, Finland, Portugal and Uzbekistan, use standard gauge. The distance between the inside edges of the rails is defined to be 1435 mm except in the United States, where it is still defined in Imperial and US customary units as approximately 4 ft 8 in.

Question: Based on this passage, what is the standard width of train tracks?
To answer the above question, the relevant sentence is: A standard-gauge railway is a railway with a track gauge of 1,435 mm (4 ft 8 in). Therefore, the final answer is 1,435 mm ( 4 ft 8 in ).