Why the most important part of a rapid transit network is your local bus

I ran a quick GIS analysis to illustrate the importance of connective public transport networks for rapid transit.

This first image shows the walking catchment of Auckland’s rail and busway stations. The coloured rings are isochrones, five-minute bands around the stations showing how far you can get on footpaths. The last band in orange shows the parts of Auckland that are within twenty minutes walk of a rapid transit station. Twenty minutes, or around 1.2km, is around the longest most people would consider walking to get to rapid transit.

Figure 1: Parts of Auckland within 20 minutes walk of a rapid transit station

This is not bad, that walking catchment shows the rapid transit serves a lot of areas directly, including the City Centre and other major centres like Manukau, Henderson, Newmarket, Sylvia Park and New Lynn. So, a lot of major employment, education and retail areas are within walking distance of a train or busway station. The walk catchment also covers off quite a few suburbs with rapid transit access, pretty much everything along the Western and Southern train lines and large areas around the Eastern Line and Northern Busway.

But clearly, most Auckland’s residential areas and a lot of its employment zones aren’t within walking distance of rapid transit. I did a quick plan on the back of a napkin and estimated it would take at least a dozen extra rapid transit lines and over a hundred new stations to get a station within walking distance of 90% of Aucklanders. Clearly that would be an enormous task to achieve.

But of course, walking isn’t the only way you can get to the station. Auckland has a very extensive bus network that already reaches over 90% of Auckland residents, and all but one station has connecting buses. So, I reran the catchment analysis using the current bus routes that serve rapid transit stations to see how far you can get by bus within twenty minutes, including five minutes for the transfer time. The difference is huge!

Figure 2: Parts of Auckland within 20 minutes bus ride of a rapid transit station

In terms of land area, the bus catchment is three times the size of the walking catchment. That alone shows the value of an integrated rapid transit network. However, analyzing those catchments with census data puts useful some numbers on the difference.

Only one-quarter of Auckland residences are within the twenty-minute walking catchment of a rapid transit station. However, a full two-thirds of Aucklanders already live within twenty minute’s bus trip of rapid transit. Similarly, about half the jobs in Auckland are within twenty minutes-walk of a rapid transit station, which is good, but three-quarters of job places are within twenty minutes feeder bus trip, which is awesome.

This data shows that in a city like Auckland, an integrated network approach to rapid transit is essential, because the feeder bus catchment covers two and a half times more residents, and three times the jobs and development opportunities than the catchment of the same amount of time spent walking to the station.

This last map also shows that there isn’t actually that much required to close off the gaps in rapid transit coverage with an integrated network approach, and that Auckland Transport’s current rapid transit development plans would do it.

The Eastern Busway and A2B busways would fix the eastern side of the map, while the proposed Northwestern and Upper Harbour corridors would do the west. The City Centre to Airport corridor would close the gap on the central isthmus and southwest suburbs, while further improvements to the Northern Busway, including tweaks to bus access into Akoranga and an interchange station at the foot of Onewa Road, would cover off the gaps on the North Shore.