At the Kenworth plant in Mexicali, four young men are busy attaching coloured plastic tubes to two lengths of steel that will soon form the chassis of a lorry destined for the US market. At the other end of the huge air-conditioned factory, others are putting the final touches to a row of huge freight haulers, each one a different colour: powder blue, metallic purple, retro orange and olive green.

In the past few years Kenworth's Mexico operation has become so efficient that the plant turns out 62 vehicles a day - equivalent to one complete lorry every eight minutes - even though its official installed capacity is only 60. Without skipping a beat, the production line can incorporate one or more of 8,000 customisations, including even the name of the customer's wife or girlfriend on the exhaust covering.