Unclogging Adelaide’s north-south corridor: Mk II

In the previous part on Adelaide’s north-south corridor, I discussed an idea about upgrading James Congdon Drive to freeway standard and building a tunnel from Mile End to Regency Park to provide a non-stop north-south route between Everard Park and Regency Park. In this part, I will continue discussing the provision of a non-stop section of the north-south corridor between Edwardstown and Clovelly Park.

Between Edwardstown and Clovelly Park, South Road forms the north-south corridor with two lanes in each direction, turning lanes and a median strip. The quality of the road is generally better than its northern counterpart between Everard Park and Regency Park. However, around Edwardstown there are a number of intersections within close distances of one another. There are five sets of traffic signals within a 1 kilometre stretch of South Road, resulting in lots of stop-start traffic at busy times.

Looking north along South Road from the pedestrian crossing at Castle Plaza towards Raglan Avenue (nearest set of lights) and Ackland Street (furtherest set of lights). This photo was taken at 2pm on a weekday.

As part of a proposed TOD including Castle Plaza, one suggestion that has been put forward has been to remove the intersection at Raglan Avenue and South Road, by changing access to Raglan Avenue to left-in and left-out only. This would force traffic that currently turns right from South Road into Raglan Avenue to turn right at a realigned Ackland Street to the north instead. This still leaves four intersections in close proximity to one another if this plan does come to fruition.

The section of South Road between Daws Road and Ayliffes Road near the former Mitsubishi Tonsley Hub generally has free flowing traffic. During peak times, long queues can form at these two intersections on both South Road and the crossroads. Building a long tunnel between Edwardstown and Clovelly Park, emerging at Main South Road beyond the Ayliffes Road intersection would allow continuous traffic flow bypassing a section of South Road where there can be a lot of stop-start traffic. Similar to the northern tunnel I previously suggested, two twin tunnels with two lanes each would be used to form the underground bypass.

At the southern end of the tunnel, the tunnel entrances would be formed by large excavations along what are currently the middle lanes of Main South Road. During construction, the city-bound lanes would be relocated to the north several metres to provide space for the tunnel entrances. Three-lanes would be maintained in both directions at all times to minimise delays. Currently, Main South Road has four lanes for traffic in each direction. After building the tunnels, two of these lanes would serve the tunnel with the other two serving Ayliffes Road and South Road traffic.

The location of where the tunnel would be located (roughly) is indicated by the green line. The northern end would be north of Ackland Street in Edwardstown and the south end just beyond the Ayliffes Road/Shepherd's Hill Road intersection. (Source: Nearmap)

At the northern end of the tunnel at Edwardstown, finding an appropriate location for a tunnel entrance is trickier as there are buildings very close to the road along the entire section. This would most likely require numerous property acquisitions to make the plan workable, which would likely come up against opposition. Not knowing what the soil conditions in the section of South Road in Edwardstown are or where placing a tunnel entrance would cause least disruption makes this an area that would need to be investigated further and more carefully.

Providing a tunnel between Edwardstown and Clovelly Park is an expensive solution to ensuring free flowing traffic on a north-south corridor, but with plans to upgrade the corridor at Darlington a few kilometres south and a study into improving traffic flow on South Road further north currently under way this section of South Road could quickly become the new achilles heel of the route if nothing is eventually done to improve it. In addition to providing benefits to users of South Road, it would also encourage some users of Goodwood Road to use the tunnel instead of Goodwood Road. Goodwood Road could then potentially be reconfigured to provide a more pedestrian friendly layout to benefits businesses along the road in a similar fashion to how Prospect Road in Adelaide’s northern suburbs has been redeveloped.

(It should be noted that this is not an official proposal, it is merely an idea and vision for improving the flow of north-south traffic across metropolitan Adelaide taking existing projects into consideration.)

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7 Responses to “Unclogging Adelaide’s north-south corridor: Mk II”

  1. Nick of Utopia Says:

    Not a bad suggestion, what provisions are there to get cars out in the case of an emergency food for thought. I still think an elevated freeway should also be considered, you could probably do it with the exting width of road, i doubt the support pillars would need to be any wider than the ones holding up the overpass at cross roads.

    • Andrew Says:

      Hi Nick, you raise some valid concerns which also have me thinking.

      Even though building a tunnel under this section of South Road would avoid a lot of the property acquisition required for other options, there would still need to be structures associated with the tunnel constructed at ground level. They include emergency escapes as you mention and also structures to release vehicle emissions from the tunnel. Those things could create a lot of unease and opposition within the community but are, unfortunately, unavoidable when dealing with a well developed corridor such as South Road.

      In an emergency, it’s more important for people to be able to escape rather than vehicles – vehicles are replaceable, lives are not. In a twin tunnel situation such as the one I envision, the escape route from one tunnel is often the other tunnel via cross passages. Some also include exits from the tunnel to street level via emergency stairways.

      An elevated freeway is an interesting option and definitely one worth considering in my opinion. It’s certainly possible from what I see with a number of modifications along the centre of South Road, but I can’t imagine how it could be constructed without causing excessive disruption to South Road traffic, one of the main reasons why I still prefer the tunnel option – it would still cause disruption, but not as much as building the elevated roadway. Modern construction techniques allow road deck segments to be assembled on columns from above without causing disruption to traffic, but it would be the construction of the columns that would cause the most disruption – and there would be a lot of them.

  2. Matt Says:

    I live close to South Rd in Clarence Gardens and I have often thought that an elevated road is the best solution. Yes it will cause disruption during construction, but as you point out so will tunnels. Let’s face the facts, whatever solution is employed it’s going to create major headaches during construction and the longer it’s delayed the worse it will become. I like what you are doing with this site, it’s good to see people thinking about alternatives and putting it out there.
    The way I see it is that at the southern end, some of the land at the former Mitsubishi site can be used to create an interchange, then it should be elevated all the way to Emerson with main exits at Daws Rd and Castle Plaza. It could probably still be two lanes each way at ground level. Ideally, in my opinion, the Galipoli underpass should never have been built and it should have been elevated all the way to the port river expressway, but obviously the collective genius that is the government thought otherwise. After all, what do I know? I just use the damn thing every day…
    Oh if only they didn’t scrap the MATS plan in the 60’s…..

    • Andrew Says:

      Hi Matt,

      The construction of the Gallipoli Underpass has created some interesting issues along South Road. While it certainly has reduced waiting times at the Anzac Highway intersection the delays have simply shifted north and south to other sections of South Road where there are still many at-grade intersections. I don’t see the construction of the Gallipoli Underpass as an obstacle to a future solution, if anything, I could see it being incorporated into one with a few changes to the road layout. However, it should have been incorporated into a greater plan for the corridor instead of being built as a stand-alone solution.

      Building an elevated roadway is possible, but there’s a number of obstacles that would have to be dealt with. Emerson Overpass would need to be altered to connect with the elevated road, and South Road between the Emerson Overpass and Gallipoli Underpass would need to be reconfigured – an elevated roadway would need to be very high to pass over the new tramway overpass, but I don’t think that’s necessary. The biggest obstacle I can see to an elevated roadway aren’t technical challenges though – it’s getting local community and business acceptance of having such a large visible structure nearby.

      • Matt Says:

        Hi Andrew
        Yes that section between Emerson and Gallipoli is a tricky one, and I think if an elevated approach is adopted then it’ll probably have to briefly drop to ground level on that whole section (as it will need to do for the underpass anyway). If so, then obviously all those streets will lose easy access to South Rd, but in the grand scheme of things that’s probably an acceptable sacrifice.
        You also raised the obvious issue of community and business support, which is probably in some ways more of a difficult subject than the engineering challenges! Especially in a place like Adelaide where it sometimes seems that negativity towards progress is more prevalent than in other cities. In my opinion, people need to face reality and realise that we are a growing city, and this is a necessary evil of urban growth. If they don’t like this fact then they might want to consider moving to the country. That might sound brutal, but if they keep stifling progress with attitudes like that then Adelaide will never grow and in fact it’ll probably go the opposite way, with more jobs and people moving eastwards. But then again, that’s probably what they want….

  3. Tom Says:

    Hi Andrew, firstly I think your blog is great and like how in depth you consider different infrastructure concepts. Just wondering what your thoughts are on your Clovelly Park-Edwardstown tunnel idea now that the Darlington interchange has been shelved? Also curious what you think of the Southern Expressway duplication without it? As someone who travels Sturt Road to Flinders often, I can only see traffic getting much worse there when the duplication is completed.

    • Andrew Says:

      I think the shelving of the Darlington interchange is disappointing and will come back to bite the decision makers in the future if it is not eventually upgraded. Considering upgrading the rest of the South Road corridor will eventually run into the billions of dollars, the $75 million required to grade separate this intersection is almost a drop in the ocean.

      On the Clovelly Park-Edwardstown tunnel issue, I definitely believe it should still be built, but clearly it won’t be as effective if the two intersections at Sturt Road and the Southern Expressway at Darlington remain as they currently are. The Southern Expressway itself won’t be as effective without the interchange either as there will be wasted capacity resulting from the existance of the junction there.

      With regards to unbuilt pieces of infrastructure, it will be interesting to see what happens at the other end of South Road with the Superway under construction. It’s a great piece of infrastructure that will benefit the surrounding industrial areas. However, the south end just funnels traffic towards the existing Regency Road/South Road intersection, which will become the next bottleneck once the Superway opens.

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