Of major concern is recent calculations that show that passengers who terminate at Chatswood 50% will not fit on the next train to city. In fact, it could take three trains to clear the backlog (not sure what happens if another North West Rail Link train arrives before the passengers are cleared). The worry concerns the safety of passengers on Chatswood Station due to overcrowding.
Another concern is that the tunnels being bored will only accommodate single deck trains. This means that ,in the future, double-deck carriages would not be able to use the tunnels.
There is a comprehensive analysis of the problems and possible solutions at: