Monday, April 25, 2011

Turning Radii and Effect on People Places

You many recall the other day I took the time to map all of the places in downtown and uptown Dallas where outdoor dining was possible. The thinking goes like this, you have a place that is a people magnet. It is a magnet because it is an enjoyable place to spend time. Meaning it is attractive. Businesses then want to capitalize on this impulse to sit and enjoy the day outside, people watch, peruse a paper, whatever, but BE THERE in that place. The outdoor chairs and tables are then an indicator of a quality place.


The next question might be, but why in these places and not others? As with all things "urban," there is rarely a singularity of answers, but a series of overlapping, occasionally conflicting, ones. When I talk about places being either attractive or repellent, these are generally objective in the coarse-grained knob. As in, what humans find amenable or not is generally universal, but to what degree, the fine-grained knob on the microscope, is subjective.

Princeton professor Anton Nelesson has been putting together visual imagery surveys for years and years and years, like the following:


This image gives you an example of how we find some places attractive (a positive response) or repulsive (negative). As this blog post by Nathan Norris suggests, there is a economic value increment to places that are attractive, ie people show up.

But it is still more complicated than that. For example, in the outdoor cafe map we see more dots in the West End than in the Main Street district. Would anybody, particularly downtown (or even Dallas) residents say they like West End better than Main Street? I doubt it. In fact, as I said in the cafe post, all places are either trending up or down. We must add more layers.

Another way to understand quality of place is by understanding its access. Two concepts come to mind being propinquity (or the location of stuff in proximity) and convergence (the centrality of a place). The first is important because if there is a significant population nearby local access is likely strong. People can walk there. Furthermore, it is likely stable as neighborhoods are more stable than businesses.

In conjunction the two concepts strengthen the local and global access of a place. Local connections are important for neighborhood centers, global access (or at least regional), makes for larger destinations on the food chain of commercial clusters. Access is important as this Space Syntax presentation points out that 80% of retail businesses cluster in the 20% most accessible places.

But too much global access can easily disrupt local connectivity, particularly car-oriented access as it tends to be the form of transportation in most direct conflict with pedestrian activity. And because, as shown above, we rate these areas lowly in attractiveness, value is almost assuredly going to wane.

One way to measure this is through turning radii of curbs and streets. As Andres Duany has summarized for pedestrians to cross streets with increased turning radii, pedestrians now must cross twice the distance and avoid cars going twice the speed.

This image from the US DOT usefully shows an 18-wheeler driving on a city street. Unwittingly, making my point. First of all, 18-wheelers don't belong on city streets, but we engineer our streets to accommodate them. Or other types of service vehicles like delivery trucks or emergency response equipment like fire trucks. All of which can be scaled appropriately to place. Instead, we let the tail wag the dog.

Have you ever been walking downtown and waiting for the pedestrian light to give you the go-ahead and even once it does, cars are rolling through right-hand turns without stopping? This can generally only happen with radii that are too large. With smaller curb radii, cars must invariably stop.

Similarly, what we often call "suburban, loopy-doopy roads" (technical term) are also designed for cars to proceed at high-speeds. Neither of these designs give any thought to the pedestrian, let alone priority to the more at risk form of transportation. I say at risk for two reasons. First, is that obviously if car and pedestrian run into each other, the pedestrian is likely going to be the one injured. Which brings about point 2: because the pedestrian is more in danger, the smaller form of transportation always disappears when the larger is given priority.

If, based on the evidence of where cafes emerge as well as guided by Anton Nelessen's visual preference surveys that nearly always rate car-oriented places as negative places to be, we can map places with car-friendly streets with the assumption that, "these are probably unlikely to be areas of pedestrian activity. And furthermore, not only will they not have pedestrian activity, but they will have a negative impact on everything immediately around them as well.

So I mapped areas of downtown with overly large radii and we get the following map:


I limited the graphic strictly to city streets and the on/off-ramps to highways, meaning I didn't bother mapping the highway turning radii, b/c, well, of course.

Here it is with the cafes also mapped:


You can see that for the most part, the cafes avoid red areas. With the notable exception of Victory. And perhaps just maybe we can see one of the reasons why Victory has and will continue to struggle, mostly because of its isolation brought about by the car-oriented nature of the streets and blocks all around it.

And lastly, here is the map with curb cuts overlaid. Curbcuts could be compared to a storefront, except the complete opposite. Both are designed interfaces between movement and place, street and building. But, if the predominant movement is designed for cars, yup, of course we're going to have curb cuts. And indeed, more curb cuts than storefronts, which are the design response to walkability, unless you like cars crashing through your windows.

The next step will be to map all of the storefronts that engage the streets in downtown Dallas. My guess is we'll continue to see a similar pattern. That the active storefronts will be in the few areas that remain for the pedestrian. These maps show that all of our places of value are constricted. Meaning the value of our city itself is also constricted and likely going to wane unless we do something about it.