Why do iron-wheeled metros and rubber-tyred metros exist?

The historic iron-wheeled metro represents 90% of the world’s existing metros. The others are rubber-tyred metros, which were introduced after 1946. While the iron-wheeled metro is the obvious choice in most cases, the rubber-tyred metro may also be used to meet specific constraints or priorities on the network.

Why do iron-wheeled metros and rubber-tyred metros exist?

While the historic iron-wheeled metro represents 90% of the world’s existing metros, the rubber-tyred metro may be a solution in some cases. Metros with iron wheels are ideal for reducing energy consumption (low friction), providing lots of capacity (high weight limit) as well as economically. The rubber-tyred metro is an obvious choice when extending existing networks (e.g. lines 1 or 14 in Paris) or in special cases such as the presence of steep slopes or the need to minimise infrastructure vibration, thanks to its strong grip and the flexibility of the tyre.

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