The Urban Network

A few years ago Peter Calthorpe, one of the leading urban designers of our generation, was looking at a bunch of the tools that are advancing good urbanism today (like the Transect, Context-Sensitive Streets, and SmartCode) and felt that something was missing. What we needed, he argued, was a pattern for holding these things together on a regional level that could easily connect to or fill-in the existing 1 mile major thoroughfare grid system that nearly every American city was using as the basis for it’s transportation plan. Houston has perhaps one of the best examples of such a plan, in its Major Thoroughfare and Freeway Plan.

[serialposts]The problem with these 1 mile grid patterns is that they provide enough investment in the areas surrounding a major city to create very spread out growth, but they don’t help create the well connected, diffuse transportation network that is critical as an area develops further. So, while the 1 mile grid works well in rural and lightly populated exurban areas, it quickly becomes strained as development reaches suburban densities, and is completely overloaded as development reaches urban densities.

The best local example of this is to compare Uptown and Downtown. As we all know, traffic is incomparably worse in Uptown than it is in Downtown. Downtown has more of everything: more streets, more freeways, more transit, more pedestrian use. The most important part, though, is that Downtown has the grid, and Uptown does not.

Uptown is a lot less dense than Downtown, and yet it’s reaching a breaking point. There are critically few ways in and out, and even though those are mega-roads, they concentrate traffic BY DESIGN rather than diffusing traffic as the grid does. If Uptown had a fine-grained local street grid the traffic there would be a fraction of what it is today, but it’s too late to put in a grid now. The best we can hope for is for benevolent developers to include new connecting streets to break up some of the super-blocks when they come up for redevelopment.

Calthorpe recognized that this phenomenon was happening everywhere, and decided that we needed a better transportation planning concept that included a more connected local street network in order to prevent the emergence of even more problem areas. He called this idea “The Urban Network,” and published an article describing it, which you can view here.

Calthorpe's Urban Network

The Urban Network adapted to local terrain

This concept is pretty useful for designing a transportation plan that not only helps alleviate traffic congestion, but also helps create walkable, transit-serviceable neighborhoods, and preserves green space around neighborhood edges. In other words, it creates an urban fabric that can seamlessly grow over time from lightly developed residential areas to core urban areas, if that’s what the market demands.

One of the critical features is the classification of context-sensitive streets ranging from transit boulevards and major through ways down to local streets. This can save the city money in construction and maintenance cost (by avoiding over-building) as well as improving quality of life.

The concept as shown is an extremely rigid grid, but in reality it would be adapted to fit the surrounding terrain. Of course, Houston doesn’t have mountains to go around, but we do have a lot of streams and waterways that are sensitive and should not be paved over. The second image is an illustration from Calthorpe’s article where the pattern is adapted to fit an area in Western Australia.

Now, his map colors indicate the network being adopted in an area with conventional zoning, and clearly Houston wants nothing to do with that. The golden opportunity, however, is to design such a system using a transect-based approach (illustrated below). Use city streets (and the city street plan) as an investment tool to create vital neighborhood centers.

Sprawl opponents should not fear this kind of strategic investment. As long as the city continues to grow, some portion of that growth will go to the edges. That’s the natural way of humans, and it’s not going to change. The goal should not be to stop the development of the edges of the city, it should be to shape that development into sustainable communities. If we use our infrastructure and our infrastructure plans wisely we can keep growth compact and continuous, while preserving key ecological areas and corridors.

The city already has the tools at hand to implement this as an infrastructure plan. Why not change the Major Thoroughfare and Freeway plan to the Urban Network Plan? It could serve as a tool both for planning the development of new areas, and infill and densification of older ones. In new areas the use of context-sensitive design can help us to avoid building mega-roads where they won’t be needed, and help ensure that the street patterns that are created are highly connective and adaptable if the area becomes a major hub in the future. In older areas we can identify where streets are not supporting the surrounding development very well and take steps to improve them, and we can also identify areas that are lacking in connectivity and work with developers to connect streets whenever possible.