Express services will run more frequently on Sydney's congested Western Line at peak periods after the Baird government awarded a $1.7 billion contract for the purchase and maintenance of 24 new Waratah double-deckers.

A day after a damning Auditor-General's report into the government's handling of Sydney's $2.1 billion light rail project, Transport Minister Andrew Constance highlighted the impact the extra Waratah trains would have on boosting capacity on the city's commuter rail network, which has faced a 10 per cent surge in patronage over the past year.

"What we're seeing in terms of growth is off the charts and we have to act quickly to keep the system running well," he said.

Mr Constance said the new trains would be used to help provide four extra express services between Parramatta and Sydney's central business district in the morning and afternoon peaks. That equated to a service every three minutes, or up to 20 trains an hour during the busiest periods.