A number of bus routes from Sydney's north will no longer extend to the CBD, forcing commuters to switch to other services earlier in their journeys to get to the city.

Transport officials say the changes to the network from next Monday are aimed at helping reduce congestion on roads in the CBD during peak periods.

The rejig coincides with the end on Monday to free travel on Sydney's public transport network for commuters who make eight journeys in a week. Instead, they will pay half-price fares for trips after eight paid journeys.

The bus services affected by the latest changes are those from Northbridge and Castlecrag, as well as some routes via Epping Road, Lane Cove and the Pacific Highway.