A tunnelling expert says it would be possible to build a tunnel under Macquarie St

Would it be possible to build a tunnel under Hobart? It’s the question being asked after Monday’s gridlock, and it’s not the first time the idea has been raised for the city.

Tasman Bridge, Hobart. Picture Chris Kidd

MONDAY’S gridlock caused by the truck crash on the Tasman Bridge has reignited debate around Hobart traffic solutions including ferries, light rail, a western bypass and even another bridge.

Another solution proposed in recent years has been a tunnel under the city.

In an opinion piece for the Mercury in 2021, tunnelling expert Tony Peach said it would be possible and preferable to build a duel-carriage tunnel below the alignment of Macquarie St.

“The distance from the Southern Outlet intersection with Macquarie St to the southern end of the Brooker Highway is approximately 2100m. If a bypass tunnel was built to parallel this route, it would require only two minutes and six seconds at 60km/h to travel across the city.

This is substantially better than the 10 to 15 minutes duration that transit of this route in current peak hour demands,” Mr Peach wrote.

Tony Peach believes tunnels under the CBD would be effective solutions to solving Hobart's traffic problems. This includes a shallow tunnel option under Macquarie and Davey streets linking the Southern Outlet to the Brooker Highway and to and from the Tasman Bridge.

“The tunnel “roof” would be a reinforced concrete deck, laid at the current surface of Macquarie St, using half the available street width while simultaneously diverting the traffic to the opposite half. Parking would have to be removed during this period of construction.

The advantage of this concept of construction is that excavation equipment could be mobilised with almost no delay, most of it is already available in Tasmania, and local contractors are adept at surface excavation and then the burying of pipelines, for example.”

Mr Peach wrote that disadvantages of the approach would be the sewer, water, telecommunication, electrical-power and other services that likely crossed Macquarie St near the surface.

He wrote that while the process would likely be “tediously slow” it had been used for the 1.7 km tunnel section of the Graham Farmer Freeway in Perth that was completed in 2000.

Mr Peach is a retired engineer who has been involved in the design and manufacture of tunnel boring machines in Australia and internationally

In an opinion piece in today’s Mercury, urban geographer and transport economist Bob Cotgrove said projected Hobart population growth of 50,000 in the next decade meant the city would need a new Derwent bridge in addition to a western bypass.

A western bypass has already been ruled out by the state government after a feasibility study, and there are no plans to build another bridge.