A dozen people were killed after Australian National Line's 11,000-tonne bulk ore carrier, Lake Illawarra, crashed into the 1.4-kilometre bridge in bad weather on Sunday, January 5, at 9.27pm - 40 years ago.

On January 6, 1975 The Examiner reported that the ship, captained by Boleslaw Pelc, hit the third pylon from the eastern shoreline before it skidded off and hit the fourth pier, bringing down two sections and 127 metres of roadway.

Tonnes of concrete tumbled into the water and sunk the ill-fated carrier loaded with zinc concentrate heading for the Electrolytic Zinc Company.

Four cars plunged 45 metres off the bridge.

Witnesses described the noise as like "a roll of thunder".

Seven crew and five people within the cars died, while two cars were stuck hanging over the edge.

Prime Minister Gough Whitlam was forced to apologise after he prematurely said in a press conference in The Hague: "it is beyond my imagination how any competent person could steer a ship into the pylons of a bridge.

"But I have to restrain myself because I would expect the person responsible for such an act would find himself before a criminal jury."

It was later found that Pelc's incompetence was behind the disaster.

The collapse closed the main link between Hobart and its eastern suburbs for 34 months.

Tasmanian historian Stefan Petrow said it isolated 40,000 Eastern Shore residents, particularly those who worked and went to school in Hobart.

People on the western shore were slightly hindered, with the Hobart International Airport being on the eastern side.

"Instead of about a few minutes drive across the Tasman Bridge, you had a 50-kilometre drive ahead of you to get to Hobart," Dr Petrow said.

"It was disruptive for people in the short-term and a lot of people who lived on the Eastern Shore in general.

"About half of them would have worked in Hobart - [and] a lot of the primary schools were on the western shore.

"It was a pretty sparse life over there as the roads were not particularly well made to drive on either.

"There were a lot of deterrents to stop you driving if you once drove and of course buses were out of the question."

The University of Tasmania senior lecturer said river transport was initially fairly ordinary too.

"If you wanted to take a car punt at Risdon, they only took about eight cars," he said.

"Even if you had a boat, you still had to have somewhere to put it when you got to the western shore and that wouldn't have been all that easy.

"So you didn't have much choice except for the ferries, and the ferries had always been on the River Derwent going back to the late 19th century but they sort of stopped once the Tasman Bridge was actually built.

"In the early 1970s, Bob Clifford started with his ferries and it was actually the right time.

"A couple of ferries he had were the so-called 'bushranger ferries', the Matthew Brady, which began operating in 1973, and the James McCabe came in 1974 - but they didn't take many passengers.

"If you wanted to catch a ferry you had to queue up, which was frustrating for people as well.

"It was a really difficult period."

By June 1975, it was estimated that 25,581 people were using ferries to commute across the Derwent River daily.

Mr Clifford's Sullivan's Cove Ferry reportedly transported more than nine million passengers in two years.

"Clifford made his name from ferries and that was the basis of his business in the future and he just kept building ferries with bushranger names," Dr Petrow said.

"He made a great profit and the other advantage of going on the ferry - which you didn't have if you had to drive - was that you could have a drink on the ferry so they made money out of the bar as well.

"Other people could see this was a profitable enterprise so you had other people coming in with boats and ferries and there was quite a competition in the end amongst various people."

Socially, Dr Petrow said Eastern Shore residents were badly affected.

Crime rates in the east increased tenfold and inadequate transport, services and the slow rebuilding process generated frustration.

"To wake up to that site and to hear that people had lost their lives had a deflating effect," he said.

"Feeling that you were cut off from the western shore had a psychological effect.

"Not many worked on the Eastern Shore, there was very little business, people relied on ambulance and fire brigades from Hobart, most of their entertainment and even restaurants and basic things like childcare were on the western shore.

"There was a real morale drop for the people of Clarence. The warden at the time was Bruce Goodluck, who later became a federal politician.

"He made his name by really pushing government to provide more services and tried very hard to raise the low morale of the Eastern Shore people.

"He became known as the champion of the Eastern Shore and rightfully so because he did an awful lot of work."

During the $44 million reconstruction, the Tasman Bridge was widened to five lanes, which was officially finished in October 1977. A secondary bridge, Bailey Bridge at Risdon, was also built.

Dr Petrow said the Eastern Shore became more united.

"It was definitely a short-term disaster, but in the long term, it probably made the Eastern Shore.

"There was great community spirit, more enterprise over on the Eastern Shore, more amenities, better services and better roads.

"Today, only the positive effects, not the negatives are felt."'

The MV Lake Illawarra remains 34 metres below the surface.

Last October, the CSIRO released sonar mapping images of the bulk ore carrier.

■To mark the disaster's four-decade anniversary, Hobart and Clarence councils will hold events tomorrow. An exhibition on the Tasman Bridge will be opened at the Rosny Barn and a minute's silence will be observed on the bridge at 9.27pm. Hobart Lord Mayor Sue Hickey and Clarence Mayor Doug Chipman will jointly unveil a plaque on the bridge, the lights will be dimmed and the roadway will be closed between 9.15pm and 9.35pm. Frank and Sylvia Manley's famous Monaro will be on display at the exhibition.