A large drop in motorists driving into Sydney's CBD over the past four years during the building of a multibillion-dollar light rail line has opened the way for construction of a key cycleway and an expansion of permanent pedestrian-friendly space.

The City of Sydney Council is considering a cycleway along the northern end of Castlereagh Street, which will be made possible if the state's transport agency shifts bus routes to Elizabeth Street as part of an overhaul of the bus network for the start of light rail services.

Commuters will learn the details of changes to their bus services between the CBD and south-eastern suburbs about a month before the light rail line opens in December.

Cyclists may finally see a bike path extended along Castlereagh Street in the CBD. Credit:Sahlan Hayes

Express buses during peak periods will be maintained but others are set for a shake up due to the increase in capacity from trams running every four minutes in either direction between Circular Quay and Randwick from December, and on a branch line to Kingsford in March.