With the suggestion that we might finally hear something more about light-rail soon, I thought I’d put down some of the things I’ve been thinking about the project recently in relation to whether it should be built as an underground line.
Speed vs Coverage
There’s been some indications the Superfund proposal includes fully grade separating the entire route from the city to the airport.
Fully grade separated lines are the gold standard when it comes to public transport infrastructure, allowing for services to run both highly frequently and very reliably. Of course, the big downside to this is the infrastructure is also incredibly expensive to build and you only need to look at the City Rail Link to see this. At the other end of the spectrum, buses or trams sharing lanes with general traffic are generally slow and unreliable, making them not very attractive to potential users.
But there is a lot of space in-between these two ends of the spectrum. We can separate PT in both space and time to improve reliability and with the original proposal, light-rail would use both of these in the form of dedicated lanes and signal priority. These would give the trains something close to what can be achieved with much more expensive infrastructure.
A high-level description of different types of right-of-way is shown below which comes from Jarrett Walker’s excellent book Human Transit – it’s worth noting that Auckland doesn’t have any PT that is fully Class A, our rail network has numerous level crossings as well as sharing tracks with freight services while the Northern Express services currently only have a full busway for 41% of their journey from Albany, and even less from Hibiscus Coast.
The downside to building fully Class A infrastructure, like some have suggested should happen with Dominion Rd, is that it’s incredibly expensive. You only need to look at the City Rail Link to see this. Underground stations are particularly expensive and because of this, one of the most likely outcomes for Dominion Rd would be a desire to reduce the number of stations that need to be built. As we can also see with the CRL, underground stations would also take longer and be more disruptive than building light-rail on the surface.
This brings us to the classic speed vs coverage debate. Fewer stations make vehicles faster but at the same time fewer people can access them. Getting the balance right can be tricky and is influenced by what our goals are. In the case of the City Centre to Mangere line, it’s not just about providing access from the city to the airport but also about serving the communities along the way.
To highlight the issue of coverage, I’ve put together this image showing a 400-800m walking catchment from the potential light-rail stations on Dominion Rd. The image on the left shows if we only had LR stations at the three town centres along the route, such as if we were building an underground line while the image on the right shows if the other two stations as previously proposed. These would be at at about Milton Rd and Lambeth Rd. I’ve also added in a 400m catchment from the current bus stops on Sandringham Rd and Mt Eden Rd as we’d expect people living closer to those roads will continue to use those services. As you can see, the town centre only stations version leaves a lot of central isthmus unserved, especially south of Balmoral Rd. By comparison those two extra stations fill in much of those coverage gaps nicely and improve access even on parts that were within 800m.
What this means is that if we were to build a grade separated option with fewer stations, we’d likely still need to run buses of some form on Dominion Rd to provide accessibility. This defeats one of the key purposes of looking at light-rail in the first place, to reduce the number of buses. There’s also less likely to be the place-making opportunities in the town centres that light-rail offers.
As for the speed trade-off, my calculations suggest that from the middle of town to SH20, from where onwards light-rail would be grade separated anyway, a fully underground Dominion Rd option would probably save 3-4 minutes. The surface option does pull a little of that back though as if you’re travelling to one of the town centres you’re at your destination the moment you get off the train, as opposed to an underground station where you then have to make your way back to the surface – depending on how deep it is.
Is that time saving worth it for the extra cost and loss of coverage, my guess is it probably isn’t but it would be interesting for someone to calculate. It’s worth noting that the surface light-rail option is already likely to save about 10 minutes compared to the current buses so it’s not like we’re not getting good improvements already.
This also brings us nicely to the next issue
We don’t need to solve everything in one project
One thing I’ve observed over the years is a tendency to try and solve every issue for decades to come with a single project. We saw this with the CRL and we’re seeing it again with light-rail. But cities, and especially large transport networks are a by-product of evolution.
Light-rail involves a significant increase in capacity and quality for public transport on Dominion Rd and the plan, as per ATAP, is to eventually link it to the North shore, creating a second and independent rail network for Auckland – I’ve written before why that’s a good thing.
But let’s say hypothetically this isn’t enough and at some time in the decades ahead, Dominion Rd services are becoming too busy. Firstly it’s not a bad thing and it would be a sign of success and that Aucklanders are using PT much more than expected. But it would still be a problem that needs to be solved and a couple of options could include:
Just like what will be possible on our existing rail network, we could make services longer. So instead of two 33m light-rail trains joined together, we could potentially combine three together to create 99m long trains. These would be quite long but not unheard of. For example Seattle’s Light Rail, which shares many similarities to what’s planned here, is designed for up to four 29m vehicles to be combined to form a train about 115m in length. Enabling longer trains would probably require a bit more work up-front to ensure platforms will fit but that shouldn’t be too much of an issue given it’s not underground.
Build another line
In short, more lines are better than one big line that try’s to do everything and takes decades to deliver.
I get why the government and officials wouldn’t want to talk about building additional lines to address future potential capacity constraints when they haven’t even started this one but there’s no reason why this couldn’t be an option. For example, we could build light rail on another of the north-south isthmus routes, such as Mt Eden Rd. That could not only help address capacity constraints on that corridor but enable people travelling to/from south of Onehunga to be spread across more services. Alternatively, by the time this may be needed, Auckland will be a much bigger city, maybe with a population of over 3 million people. At that point we could build that underground line to enable the Orewa to Airport line to be fully grade separated (and perhaps automated) while leaving the surface level route on Dominion Rd to still serve local communities. We could even take the tunnel on a different route to give more options to our RTN network. This is shown below but the route is just for demonstration purposes, not something a lot of thought has gone into (although I did include our Crosstown light-rail idea).