The lengthy thread of comments in response to my post about the CBD Rail Tunnel on Tuesday have raised a number of questions about the details of that project that I think are worth exploring a bit further. One interesting point discussed was the issue of the grade of the tunnel, how problematic that might be, and what could potentially be done about it. As I said in the previous post, I really do think that even with only two additional CBD stations (Karangahape Station and Midtown Station) we’re pushing the limits of what is feasible in terms of the tunnel’s grade. Adding more stations could push the gradient over the acceptable limit – thereby potentially creating a rather unsolvable problem.
Previous studies into the CBD Rail Tunnel also recognised this potential problem. The URS/GHD study in 2004 provides us with the most detailed map yet of the potential alignment of the railway tunnel – although there is currently a study underway to provide us with a final design, put together a business case for the project and prepare the necessary documentation to lodge a notice of requirement. But anyway, in terms of the grade of the tunnel, the URS/GHD study suggested that this could be eased by effectively lowering the section of the western line (or at least the links between the CBD Rail Tunnel and the Western Line) around the Mt Eden station – thereby reducing the height the tunnel would need to climb to and reducing its overall grade.
This is shown in the URS/GHD map below – which also gives us a reasonable indication of where they thought the stations should be located: One interesting aspect of this alignment is that the Mt Eden station would be shifted away from its current alignment on the Western Line and actually into the rail tunnel – basically underneath Exmouth Street. I think this is a pretty good idea, as it would make it possible for trains heading to the tunnel from the west or south (or vice versa) to access the station. While the odd train from the west to Britomart via Newmarket (probably the services using diesel trains from Huapai) wouldn’t stop at this station, I don’t think that’s a big problem. Furthermore, the current Mt Eden station is located fairly poorly in my opinion – hidden away behind a bunch of buildings – while the new one could have good access off New North Road and Newton Road. It would probably need its name changed to Eden Terrace station or Newton station – but I don’t think that’s a problem.
In the diagram below is my idea for how this end of the rail tunnel could work. The green lines show parts of the track that would effectively be a lowered trench (to reduce the tunnel’s grade), while red lines are the tunnel. The extent of the station is shown, while the blue crosses mark where I think there could be entrances and exits from the station: The next image looks at the Karangahape Road station. This station would be quite deep, at around 20 metres below ground level by my calculations. The depth is necessary because at a constant grade of 1 in 35 the tunnel will be around 40m above sea level by the time it reaches the Karangahape Road ridge – whereas the ridge itself (along which the road runs) is around 60m above sea level. 20 metre deep stations certainly are not unheard of around the world, so I don’t see this as a show-stopper. However, it will be an expensive station to construct.
Once again, the red line shows where I think the tracks might go (they generally follow road alignments to minimise the number of strata titles that would need to be purchased) and the blue crosses mark possible entry/exit points: And finally, let’s have a look at the Midtown station. This station would basically be built underneath Albert Street within the block that stretches from Victoria Street to Wellesley Street. One very good thing about this station is that it could have excellent access to Queen Street via the Atrium on Elloitt shopping centre and Darby Street, which by good coincidence is going to be turned into a pedestrian mall in the near future. Midtown station is likely to rival Britomart as Auckland’s busiest station in the future – particularly as its location is right in the heart of the CBD and it is a relatively short walk from the university. The blue cross in the map below that is some distance from the station itself shows where the main entrance from the Queen Street side of the station would be – at the northern end of the Atrium on Elliott shopping centre as I stated above: I must say it certainly will be interesting to see what the current study into this project comes up with – and whether there are any significantly altered alignments from what I have outlined above.