The work, called Train, has been commissioned from Koons by the Los Angeles County Museum of Art. It is based on a 1943 Baldwin steam engine built at a plant in Pennsylvania. The engine will be 20m long, hanging from the much taller, red and yellow crane. It is expected to be finished in 2011.

The total cost of making the steel and aluminium work, which will produce its own steam and whose wheels will turn, will be an estimated £18m. This beats the £13.2m cost of the gems and platinum in the Damien Hirst sculpture For the Love of God.

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