Baltimore's Key Bridge collapse sparks memories of Hobart's own ...

Almost five decades before a cargo ship lost control and crashed into Baltimore's Key Bridge, another ship hit a very different bridge in a deadly accident right here in Australia, killing 12 people.

While rescue efforts continue overseas, news and vision of the bridge completely collapsing has taken many Australians back to 1975, when Hobart's Tasman Bridge partially gave way.

The Tasman collapse was a sudden, horrific event that left some cars hanging by their rear wheels, teetering on the edge, while others plunged 45 metres into the River Derwent.

Cars balance on the edge of the broken Tasman Bridge shortly after the Lake Illawarra disaster on January 5, 1975.(Ben Short)

A section of the Tasman Bridge fell onto the ship's deck and killed seven crew members, and five motorists also died.

The tragedy still has some Tasmanians anxious when crossing the bridge today.

Frank Manley, was driving across the bridge with his family when the SS Lake Illawarra struck the pylon.

Mr Manley, now in his 90s, still remembers it well.

"I was approaching the bridge and the lights went out and I thought there was an accident on the bridge," he said.

He recalls another car overtaking him but it had disappeared when he reached the crest.

"The next thing, the wife said, 'The bridge is gone! The bridge is gone!' I hit the brakes, I didn't think I was going to stop."

Mr Manley said he scrambled quickly out of the car while his 16-year-old daughter ran to warn an approaching bus.

"I had a steel watch band on. You still see the scratch on the roof of the car where I put my hand on the roof to balance myself to get out towards the back of the car."

Mr Manley's Monaro is now on display in a Launceston museum.

Frank Manley recalls his wife yelling "stop, stop" as the bridge collapsed in front of them.(ABC News: Phoebe Hosier)

The Tasman Bridge is the main connection between Hobart's eastern and western shores — so when it collapsed, the city was split in two.

Within hours of the crash, ferry services were running. Around a year later a temporary modular bridge was built, saving locals a long round trip to the other shore.

But the two sides would not be properly reunited until two and a half years later, when the bridge was finally rebuilt.

SS Lake Illawarra still lies on the river bed next to the Tasman Bridge pylons.(Supplied: CSIRO)

Engineer Bill Lawson told local ABC local radio how the designs of the two bridges are vastly different.

While the Tasman Bridge is prestressed concrete, Baltimore's Key Bridge was a steel truss bridge with interconnected spans.

"The spans of Tasman Bridge are quite separate to each other … so designed to stop one pulling down the other," Mr Lawson said.

"It gives everyone in Hobart a reminder really how vulnerable the bridge is and there's good reason for stopping the traffic when a ship goes through," he said.

"We're lucky that we're looked after by the traffic lights that stop us."

The Tasman Bridge is supported by massive concrete pylons.

The Hobart event led to major changes to river traffic rules – including the stopping of bridge traffic while ships pass under, and larger ships are now escorted by tugs.

All vessels must be piloted too, which wasn't the case in 1975 – a thought that haunts maritime pilot Digby Longhurst, who was not required to work on the SS Illawarra that night, and was asleep in bed at the time of the collision.

Under the rules back then, a captain could proceed without a pilot if he had navigated the port in the past two years – which Mr Longhurst called a money-saving measure for the owner of the ship.

An inquiry found the SS Lake Illawarra was off course due to river currents and inattention when the ship struck the bridge.

SS Lake Illawarra, the bulk carrier which crashed into the Tasman Bridge in 1975, in Hobart.(Tasmanian Archives and Heritage Office)

INCAT ferry chair Bob Clifford, who started ferrying people across the River Derwent after the Tasman bridge collapse, said safety was a "major ingredient" these days.

He said his ships travel under the bridge two or three times a year, with extra engines to fall back on if one fails.

"You always have two generators online in case one was to go down.

A view of the Lake Illawarra resting under the Tasman Bridge.(Facebook: UTAS Life)

"Then most of all, of course, the anchor is ready to drop, which will not necessarily save the ship but may save the bridge. So all in all, there are many, many safety devices that we have to abide by, and quite rightly so."

While authorities are still investigating what caused the Baltimore crash, preliminary investigations point to an accident, with Maryland's governor saying the ship's crew alerted authorities to "a power issue" before they crashed

The wreck of the SS Lake Illawarra still rests on the river bed below the Tasman Bridge.

The CSIRO and engineers 3D mapped the wreck in recent years, believing it could help inform any upgrades to the bridge.

The highest point of the ship rests just 15 metres below the river's waterline, while the 140 metre-long bulk carrier's bow lies next to the third pylon on the eastern shore side of the bridge – the ship pointing at a 45-degree angle towards the middle of the river.