Elevated highways

[kaska]

Should Adelaide Consider Elevated Highways Instead of Multi-Billion-Dollar Tunnels?

I’ve been following the Torrens to Darlington (T2D) tunnel project closely, and while it’s an impressive piece of infrastructure, I can’t help but question whether a more cost-effective and faster approach for the next necessary highways for the city — elevated expressways, like the kind used extensively in Taipei, Taiwan.

A Proven Model: Taipei’s Elevated Highways
Taipei has built an expansive inner-city network of elevated highways — like the Civic Boulevard Expressway and Jianguo Elevated Road — running above arterial roads with minimal disruption to existing structures. These are supported by reinforced concrete pillars and often include sound barriers to reduce impact on nearby residents.

In many parts of Taipei, these highways run above or alongside commercial roads, which helps reduce residential impact and integrates well into the urban fabric. Despite some visual bulk, they’ve proven incredibly effective at reducing surface congestion without the monumental cost and complexity of tunnelling.

This could be the case in Adelaide, some major avenues are purely commercial.

Cost Comparison:
Taipei-style elevated expressways: approx. $50M–$150M per km

T2D tunnel project in Adelaide: approx. $940M per km

That’s up to 20x cheaper — and construction is dramatically faster and less risky.

Speed & Construction Impact:
Elevated highways are built faster, don’t require complex underground boring, and are less affected by unknown utilities or soil conditions.

They can be prefabricated, with columns and decks assembled off-site and installed with minimal street closure.

When aligned along commercial corridors, they avoid the NIMBY backlash tunnels often receive when surface disruption hits suburban streets.

Pros & Cons:
Pros
6–20x cheaper than tunnels
Much faster to build
Less disruption to utilities
Proven model in high-density cities
Can run above commercial corridors

Cons
Visual intrusion
May increase perceived noise (even with barriers)
Could affect property values along corridor
Aesthetic concerns (unless architecturally integrated)
Requires strong public engagement

It is clear that Adelaide traffic is only going to get worse, even after the Torrens to Darlignton tunnel is finished. What will be our next move? Another 15 billion dollars project? or several elevated highways that are faster to build at a fraction of the cost?

Would love to hear your thoughts.

[Nort]

We have built several kilometers of elevated highways where the conditions were suitable for them. If you look at the areas the tunnels are being built the current width of South Road wouldn't be suitable for them, so you have the massive property acquisition costs accompanying that.

[[Shuz]]

Yeah, nah.

[rev]

This is Adelaide, not an Asian metropolis.

What you see in those photos is not what the Adelaide suburban landscape looks like.
Those people when at home, are confined to their apartments.
We have mostly detached dwellings, it simply would not work here. That's why the only elevated part of the NSM is through an industrial area.

[Llessur2002]

If you search the forum you'll find the debate over tunnels vs surface roads vs elevated roads has come up many, many times before. My personal opinion is that in an ideal world I'd prefer none of them, I find them just about acceptable in industrial areas and completely unacceptable in residential areas. Where new large roads need to be built through residential areas I'm comfortable with the extra tax dollars being spent on tunnels. Our kids and grand kids will thank us.

[[Shuz]]

Although it is interesting to note that they have been seriously considered as part of the NS Motorway between Cross Road and the Southern Expressway.

When I worked at the transport department over a decade ago, there were full detailed plans for an elevated freeway above the Seaford/Tonsley rail corridor.

Understandably, and rightly so, this idea was shelved.

[Nort]

Although it is interesting to note that they have been seriously considered as part of the NS Motorway between Cross Road and the Southern Expressway.

When I worked at the transport department over a decade ago, there were full detailed plans for an elevated freeway above the Seaford/Tonsley rail corridor.

Understandably, and rightly so, this idea was shelved.

Guess for some of those things it makes sense to do detailed plans to understand the reasons why they aren't a good idea.

[rev]

If you search the forum you'll find the debate over tunnels vs surface roads vs elevated roads has come up many, many times before. My personal opinion is that in an ideal world I'd prefer none of them, I find them just about acceptable in industrial areas and completely unacceptable in residential areas. Where new large roads need to be built through residential areas I'm comfortable with the extra tax dollars being spent on tunnels. Our kids and grand kids will thank us.

I think they're unavoidable and necessary, motorways/freeways that is in large cities. We're behind the eight ball on building these anyway compared to other large developed cities, this is a catch up that's long over due.
But in an ideal world I think they would be built not right up against homes with some lame barrier/wall and a few trees planted, but with a wide green reserve between the motor/freeway and homes.
And I think more could be done to reduce the noise impact, be it from finding better construction materials - types of bitumen that reduce road noise, or better regulating vehicles particularly heavy vehicles.

[Llessur2002]

If you search the forum you'll find the debate over tunnels vs surface roads vs elevated roads has come up many, many times before. My personal opinion is that in an ideal world I'd prefer none of them, I find them just about acceptable in industrial areas and completely unacceptable in residential areas. Where new large roads need to be built through residential areas I'm comfortable with the extra tax dollars being spent on tunnels. Our kids and grand kids will thank us.

I think they're unavoidable and necessary, motorways/freeways that is in large cities. We're behind the eight ball on building these anyway compared to other large developed cities, this is a catch up that's long over due.
But in an ideal world I think they would be built not right up against homes with some lame barrier/wall and a few trees planted, but with a wide green reserve between the motor/freeway and homes.
And I think more could be done to reduce the noise impact, be it from finding better construction materials - types of bitumen that reduce road noise, or better regulating vehicles particularly heavy vehicles.

Just to clarify that my comments were specifically in relation to elevated roads as opposed to large roads in general. But absolutely agree that more could and should be done around road projects as a whole - roadside landscaping in Adelaide in generally woeful at the start and if left to deteriorate over time, noise reduction measures are generally a token measure and not particularly effective from my experience.