As I have written earlier, I now think the best eventual option for a nonstop N-S corridor would be in tunnel beneath Morphett Road, Adelaide Airport, Findon Road and the railway to the eastern part of Port Adelaide, where it would join the Port River Expressway and Grand Trunkway. I have now added the route to the Not Investigated section of my website.
A reply I made earlier on the South Road thread was off topic there but relates directly to this, so I'm moving it here:
adam73837 wrote:
Yes there are a lot of roads in the Northern and Southern Suburbs that are parallel to South Road. Just on your comment about English Roads being upgraded in a similar way, do you think that since Adelaide is such a North-South Orientated city, it would be a good idea to include grade separations on the East-West Routes, then have the Tollway(s

) (which I'll discuss later in my post) serving the North-South Route?
No I don't. Most of the E-W routes don't have the traffic levels to justify grade separation, and we would be better off encouraging a modal shift onto public transport. A possible exception is Lower NE Road (which itself collects traffic from several E-W roads) and Magill Road together funnelling so much traffic into North Terrace (Kent Town) but even that's less of a problem as it might appear, because Fullarton Road enables some of the traffic to avoid it.
And remember we do already have one fully grade separated road (Port River Expressway) and it's also planned to grade separate Grand Junction Road at Gepps Cross.
adam73837 wrote:Aidan wrote:that's the reason why a tunnel under the City is so important.
I definitely agree that a railway tunnel under the city, like you put forward in your plan is VERY important. The benefits that it would give to the City Square Mile would be incredible. I also agree that:
Aidan wrote:the nation is in no danger whatsoever of going bankrupt. If anything it's not investing enough in infrastructure.
I agree with you 100%. My dad went to a conference several months ago where one of ANZs top bankers gave a presentation about going into debt (... or something like that

). He said that there is nothing wrong with going into debt with infrastructure which you will get a return from. An underground railway and a tollway would both generate such revenue (...eventually

).
Generating revenue eventually isn't really good enough when it's possible to get a better return on the money. The main benefits of transport infrastructure are the indirect benefits, as they would enable things to be done that wouldn't otherwise be practical. The case for tall buildings in the City would be a lot weaker if they needed to provide parking spaces for everyone.
adam73837 wrote:Aidan wrote:There was a long term plan to link Marion Road with Hanson Road. Obviously this would involve aligning it and Holbrooks Road, though quite how Holbrooks and Hanson Roads would be linked I don't know. Nor do I know if the plan is still on the official long term agenda, but it could be done if necessary.
Aidan wrote:If we do ever need an underground tollway, I now think it would be better to construct it under Morphett Road and Findon Road, serving Adelaide Airport directly.
Speaking of which, since my last 'era of posts'

I took your suggestions on board and have been doing sketches looking at different routes for such a thing. I have also been looking at books about European Cities and if there's one thing I've noticed that cities like London, Manchester, Paris, Munich and Stuttgart (which I just finished a project on in SACE Stage 1 German Continuers) is that the all have ring roads, etc.
Yes. That's something that's not practical in Adelaide because of our proximity to the coast.
Building a tollway like the one you mention to go beneath Marion Road, serve the airport, etc. then head towards Dry Creek via Holbrooks Road, East Terrace, Rosetta Street, Days Road and South Road wouldn't be such a bad idea.
Actually I think it would be such a bad idea. If it's to directly serve the airport, it's much better to run beneath Morphett Road. Joining the (duplicated) Southern Expressway at Majors Road (with an entrance from Majors Road) it would provide a route that would be much shorter as well as much quicker to all the outer suburban suburbs, and could make it easier to get to intermediate destinations such as Marion Shopping Centre.
One of the reasons I prefer a Morphett Road alignment is that it does something other than duplicate the function of South Road. Your idea doesn't seem to at all. Traffic from the Port would have to get onto South Road, and once it does that it may as well stay on South Road. Likewise for traffic from the Northern Suburbs.
it would also serve well in bypassing freight from the city
There's not much freight from the City as it is. You don't need to grade separate the roads to get the trucks to bypass it - the vast majority do already!
and, if built in conjunction with a connection to the S-E Freeway, would serve Adelaide very well. Other than these two, I don't think that Adelaide needs to be overrun with freeways like in cities such as LA

and Dallas.
Well I suppose that's an improvement from your previous view that the MATS plan would've been a good thing
An extensive and efficient PT System would 'fill in the gaps' ensuring that Adelaide comes close to regaining its status as a 20 minute city.
It should be the basis, not the filler!
Just as an after thought, do you think it would be a good idea to have 'exits' from this North-South Corridor to go along the old Glenelg Railway Corridor for the Traffic to/from the South to access the city and from the North-South Corridor to have something along Port Road for the Traffic to/from the North to access the city?
No I don't, which is why I now think the airport route is better. Getting more traffic to the City is not a desirable objective, as somewhere is needed to park, and it could cause more congestion on City streets. It would be far too disruptive to build on the surface, and the expense of tunnelling couldn't be justified. My original suggestion for a tollway route did run beneath the old Glenelg Railway Corridor to give better access to the City, because I thought it would make it easier to attract enough drivers willing to pay high tolls to make it self funding. But when a grade separated South Road also takes a lot of traffic to the CIty, attracting high tolls is unlikely to be easy. So it's better to go with the route that most improves connectivity. A Morphett Road alignment is best for that. It's due north of Panalatinga Road, but it has been a very long time since you could get directly from one to the other. Some sections of Morphett Road are closed to traffic, while others have been removed completely. Then the airport's in the way, so it can't continue north like the roads a mile on either side. These factors, along with the Oaklands crossing and the Prunus Street diversion for northbound traffic, mean that Morphett Road itself is much less busy than Marion Road, which might make constructing a tunnel under it easier. And while the airport won't attract as many regular journeys as the City, it will attract plenty of irregular ones with a greater proportion of people willing to pay.