An extra 1 million people catching trains to Sydney Airport last year has spurred the state government to put on an additional 200 services a week in an attempt to cope with the unprecedented demand.

Underscoring the pressure on Sydney's transport network, train patronage to and from the airport has risen by 32 per cent over the past two years to 8.2 million passengers in 2016.

The surge in demand has been greatest at weekends – rising by 42 per cent since 2014 to 1.8 million passengers last year.

The growth comes despite the cost of a one-way journey between Sydney's CBD and the domestic and international terminals costing an adult passenger more than $17 during peak hours, making it Sydney's most expensive stretch of rail track.