Tom Ugly’s Bridge and Captain Cook Bridge over the Georges River are the major bottlenecks slowing down commuters travelling from the south of Sydney to the CBD, a new report warns.

The report from the NRMA and the Illawarra Business Chamber says it takes the same time to travel the final third of the journey from south of Sydney to the CBD as the initial two-thirds.

It says roads south of the city have failed to keep pace with traffic growth, leaving commuters battling worsening travel times and warns that there is an over-reliance on a limited number of main roads and a constrained rail network south of Sydney.

Slow going: Morning peak period traffic on Captain Cook bridge. Credit:John Veage

"Without intervention, travels times from the Illawarra to greater Sydney will steadily increase and the cost of delays is estimated at $640 million per annum by 2031," the report says.