Improving access to the airport has been the subject of countless debates over the last few years and most recently with confirmation that the Puhinui station will be upgraded to a bus/train interchange. Sometimes those debates have resulted in claims such as that the proposed solutions of both a light rail line to the north and busway to the east won’t have enough capacity.
An early business case by the NZTA from 2017 that resulted in the Southwest Gateway programme and help shed some light on that. The business case (85MB) is out of date as the timing and scope of some interventions has changed. For example, Rapid Transit infrastructure to the east is not expected to occur till the late 2030’s yet the Puhinui announcement shows some of that is already starting to happen. While the business case itself might be out of date, there is still a lot of useful information in it that is worth sharing.
As we know, there are only two ways of accessing the airport and the commercial/industrial area, from the North (via SH20A) and from the East (SH20B). The report notes that 63% of trips come via the North and 37% by East. The graphic below highlights who it is that are accessing the airport area.
Currently just under 20 million passengers pass through the airport and there are about 28k employees. The airport predict that by 2041 this is expected to grow to about 40 million passengers and 48,000 employees. This obviously represents significant growth.
This chart gives a bit more detail on where workers are coming from or going to. The map is very busy and it’s not entirely clear but one thing that is noticeable is that it doesn’t appear all that many are near rail lines.
One of the big issues with accessing the airport at the moment is travel time variability. The peaks are becoming busier which means people are having to allow more and more time to access or leave the airport. This is shown well in this graph of SH20B. It appears to have crossed a tipping point around 2014, going from having a little bit of delay during the afternoon rush to being afternoon most of the afternoon/evening.
This is also shown in the vehicle volumes throughout the day with the peaks growing and spreading between 2011 and 2016.
Perhaps one of the more interesting graphs is this one showing arrivals and departures to the area by travellers and workers. What is notable is how the number of travellers arriving at the airport for a flight is fairly constant throughout the day but travellers leaving the airport are much more peaked in the evening at the same time as most workers are leaving.
What’s also important about this is that even with the airport set to double passenger numbers and nearly so in workers, with both light rail to the north and a busway to the east there is more than enough capacity even if all of those extra trips were to take place on public transport. That would give it a modeshare perhaps better than the city centre today.
Either way modeshare will have to change significantly as the NZTA say
There is a gap between current limited available capacity and future demand on SH20A and SH20B. These routes have already reached their capacity for lengthening periods of the day and are therefore subject to severe congestion. Projected future demand for cars journeys on these routes cannot be met.
The future transport capacity gap is significant. At current mode share proportions, even if up to eight motorway lanes are provided, 18 traffic lanes are needed by 2046 to meet demand (Figure 35). Continuing to build general traffic lanes cannot accommodate the future demand to access the airport and surrounding area.
In other words, even if we made both the roads accessing the airport the biggest motorways in the country, which would require widening most of the motorway network, it still wouldn’t be enough.
This graphic is a good example of why trips to the airport are currently dominated by cars. It shows how far you can travel within 45 minutes by public transport (blue) and car (red)
As mentioned, the business case is out of date as some of the timing is off but this graphic is good at showing how, with all of the upgrades that are planned, there will be sufficient capacity for all the growth that is coming.
This is broken down by route too. One thing I would also note is that the capacity of the East RTN seems quite low and could likely be significantly increased with additional services.