Humantransit has a great post on cul-de-sacs and what is known as the “radius of demand”. In short, the post highlights how disconnected street networks make it much more difficult to adequately serve areas with good public transport, because what should be a relatively short walk ‘as the crow flies’, becomes a really long walk to the bus stop/train station because the street network won’t allow you to make the trip in a more direct manner.
This is excellently illustrated in the diagram below. These are two real-life suburbs in Seattle. The red dot in the centre of each circle illustrates potentially where a train station or bus stop could be, with the circle being a 1km radius around it. Nothing unusual there. But what is really interesting is what the blue lines indicate – the streets which are within an actual 1 kilometre walk of the red dot. In the street pattern on the right, because there is a basic grid pattern around 64% of the “catchment” is actually within the 1km walking distance of the middle. However, in the street pattern on the left, because many of the walking trips involve convoluted detours, and the street network is poorly connected, only around 30% of the catchment is actually within that 1km walking distance to the centre. That means that the walking catchments of these two areas, while at first sight appearing equal, are actually vastly different.
This is reason number one why gridded street patterns are very useful. They improve walking accessibility to public transport stops & stations.
Reason number two why gridded street patterns are useful is when it comes to designing effective public transport networks – particularly if we’re trying to create a “network effect“. This is relatively well illustrated in a recent post I did on trying to adapt the network effect idea into a redesign of Auckland’s isthmus bus routes, where I eventually came up with this:
The idea is to create something of a “grid” of service patterns, so that north-south routes are complemented by east-west routes to create a network/web of routes allowing “anywhere to anywhere” travel. This works OK in the centre-west part of the isthmus, where the main street form something of a “super-grid”, especially around Balmoral, Mt Eden, Sandringham and so forth. But in the parts of the Auckland isthmus to the east of State Highway One it is much more difficult to achieve such an outcome, because the main streets do not form a grid, but rather seem to meander all over the place. This same issue also makes it a quite challenging to create a network effect on the North Shore (and undoubtedly also in Manukau and North Shore cities).
In contrast, if we look at Vancouver’s street pattern it’s easy to see how the network effect has worked so effectively: The main streets form a superb “super-grid”, allowing many north-south and east-west routes to operate efficiently, linking together to create a network that truly allows anywhere to anywhere travel. Furthermore, within each “super-block”, the street patterns a simple and gridded, allowing very quick access from wherever you live to both a north-south and an east-west route.
This is why I find it so depressing to see new parts of Auckland have street patterns like this:It’s not the density of recent developments in Auckland that makes them so difficult to serve with public transport, as in fact many recent growth areas are quite high density due to the high value of land. I actually think the bigger barrier is actually the street patterns that we’re seeing – like in the area above. This kind of street pattern discourages walking anywhere (as it’ll take forever because you have to travel so indirectly) and as a result contributes (along with a neglected public transport system) to making auto-dependency inevitable. I’d love to say that there has been a realisation of this in recent years, but sadly the area above is one of the newest parts of Auckland, as is the area between Albany and Greenhithe which is arguably even worse.
Street patterns matter. A lot.