Sydney motorists stuck in a citywide traffic jam on Wednesday morning probably wondered how one man climbing the Harbour Bridge managed to bring the roads to a standstill.

Traffic experts told The New Daily the harbour connections were “very vulnerable” to disruption – but said that’s life.

The 43-year-old man with “significant mental health issues” scaled the bridge about 4.30am, sparking a major police operation that closed the bridge for five hours.

Traffic was diverted to the Harbour Tunnel before the man surrendered to authorities, easing congestion by 11am.

Geoffrey Clifton, a senior lecturer in Transport and Logistics Management at Sydney University, said just four road crossings between Olympic Park and North Head made the network “very vulnerable”.

“In a sense, it is the price we pay for having such a lovely harbour,” Dr Clifton told The New Daily.

NSW Police said the man has “significant mental health issues”. Photo: AAP

He said it would not be justified to build more connections based on Wednesday’s disruption.

“We know that if we build another harbour crossing then we can add some more redundancy to the network and that is one of the justifications for the Western Harbour Tunnel, but it is not enough to justify on its own,” Dr Clifton said.

“New transport links have to stack up in terms of the extra capacity and travel-time savings every day, not just the one day when there is major disruption.”

Michiel Bliemer, from Sydney University’s Institute of Transport and Logistics Studies, said it would be difficult and inefficient to make transport networks “fully robust” against incidents.

“Of course additional connections across the harbour would have diminished the impact of this incident,” Dr Bliemer said.

“Such incidents do not happen often and therefore it is not cost effective to make our road network completely robust to such incidents.

In other words, these delays are part of life.”

Dr Bliemer said the impact was so significant on Wednesday because the bridge already acts as a bottleneck.

The Western Harbour Tunnel will connect to WestConnex at the Rozelle Interchange, cross under Sydney Harbour and connect with the Warringah Freeway at North Sydney.

In its annual audit released last month, Infrastructure Australia said the harbour tunnel needed to be developed within 10 to 15 years.

The Western Harbour Tunnel plan. Photo: Roads and Maritime Services

The design phase of the project is expected to be completed by the middle of this year.

Meanwhile, Roads Minister Melinda Pavey announced the $3000 penalty for trespassing on the Harbour Bridge would be dramatically increased.

“We need to send a message that no matter how sad their personal circumstance may be, you cannot hold this city to ransom,” she told reporters on Wednesday.

“Anyone thinking of doing anything as stupid as this … there will be a very big price to pay.

“We will be increasing that fine significantly.”

NSW Police said the man was being assessed in hospital before he would face charges.

Distressed readers should contact Lifeline on 13 11 14.

-with AAP