Overall, all the subways serve at least a billion people a year and have over ten lines. However, there is quite a disparity in terms of ticket prices and the length of the subway system differs considerably over the six cities.
Tokyo and Beijing have the two most used networks, with double the amount of yearly journeys than most of the others. They are also two of the cheapest, with only the Mexico City Metro offering a lower price which, at 23 cents, is a tenth of the cost of a journey in Paris.
Interestingly, the Paris metro has the least amount of track, at only 127.4 miles, which is less than a quarter of the 659-mile length of the New York system, yet its 16 lines are more than most of the others. The London underground has the lowest number of lines and is used by fewer people (1.2 billion journeys per year) than in any other city. Furthermore, it is by far the most expensive place to take a ride. With a ticket costing $7.30, it is almost triple the cost of a journey in New York, the next most expensive metro system.