Capacity was increased by upgrading for trains with three cars, each with four doors per side. The alternative of more frequent trains was rejected as the signalling changes needed would have cost no less than upgrading to longer trains and with fewer benefits. The railway had been built for single-car operation, and the upgrade required both strengthening viaducts to take heavier trains and lengthening many platforms. The extra capacity was useful for the 2012 Summer Olympics, which increased the use of London's transport network. The main contractor for the expansion and alteration works was Taylor Woodrow.