Sydney's new cycleways have opened

As Sydney's CBD braces for the light rail disruption, commuters are being urged to use the city's new cycleways.

Two separate lanes, built by the NSW government opened on Monday, ahead of the light rail construction that begins on Sunday.

The lanes provide cyclists with a link from Central Station to the Sydney Harbour Bridge.

Lord Mayor Clover Moore said the cycle lanes would help ease pressure on public transport and create more space on the roads for drivers.

A 12km route between George, King and Market Streets will be dug up at various stages and a new bus timetable will be introduced on October 4 as George Street shuts down.

"Around 7000 people ride to work in the Sydney city centre each day - the equivalent of 116 full buses or seven Sydney trains," Ms Moore said in a statement on Monday.

"Getting people on their bikes takes pressure off public transport and creates more space on the roads for those who need to drive."

Light rail construction is expected to take two and a half years, before testing begins in June 2018.