Transurban boss Scott Charlton has moved to quash concerns that unexpected delays to its NorthConnex project in Sydney could crimp dividend growth.

The nine-kilometre road tunnel was supposed to open by December this year, but that has been pushed back, with construction about six months behind schedule because its builders decided to tunnel deeper so they would not have to buy up properties.

Transurban's half-year earnings jumped 10 per cent to $1 billion. Credit:Jason South

Ahead of the toll operator's result, some analysts said that Transurban needed the capital releases from the NorthConnex project to support its dividends, and that the timeline for releases could be thrown out due to project delays.

But Mr Charlton said there were other sources of cash to fund dividend payouts, including from Sydney's M7, which is coupled with the NorthConnex project, and on Tuesday the company reaffirmed its guidance to pay a full-year dividend of 59¢ per share. Shares closed down 1.9 per cent to $12.22.