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In Praise of Tree Grates (Yes, really)

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Ted Rosenbaum

Former athlete, full-time engineer. I'd tell you more but I'd have to kill you.

Last fall, Scientific American made a splash with an article combining environmental biology with sustainable transportation ideas. (We're animals, after all, so this made a certain amount of sense.)  Their fundamental point was that women on bicycles are an "indicator species" for the degree to which a city is bikable (and by proxy, livable.) For city planners, this yielded very powerful advice: if you want to improve your city's bike infrastructure, make it more female-friendly.

Central St. Tree Grates.JPG

Although I don't have the extensive data at my fingertips that Scientific American did, I think there's a similar "indicator species" for the walkability of a neighborhood: tree grates.  How can this be so? Well, let's look at the four basic levels of non-industrial development we see throughout most of Chicagoland.  One is Urban Core.  Here we have busy sidewalks and extremely tall buildings.  There isn't nearly enough consistent sunlight at street level to support trees, and who wants them there, anyway?  The shade trees provide is already taken care of by skyscrapers, and the views people come to Chicago for involve towering sheer faces of steel and glass, not leaves.

On the other end of the spectrum, there are strip malls and asphalt prairies.  Here, in those rare cases where there is a sidewalk at all, it has no shade.  The sidewalks are badly underutilized because of the auto-centric nature of the development anyway, so why should the city spend the money to improve them?  Also, the streets these strip malls face often have high speed limits, and in these cases a row of trees within inches of the curb can turn into a safety hazard.  Generally then, tree grates are an indicator of slower speed limits, which enhances pedestrian safety.

In the middle, there are two types of land uses where we actually see trees at all: single-family home suburban, and denser mixed use areas.  Usually the single family homes are set back further from the curb--so far in fact, that there's room for a front yard, sidewalk, and a parkway with larger trees.  This yields nice, shady streets that usually have lower speed limits, and if there are "eyes on the street" they're probably very safe areas too.  But below this aesthetic lies more auto-centric culture.  Long stretches of un-attached homes in purely residential districts means that anything you need--groceries, a hardware store, clothes, a movie theater--is probably a car ride away--probably to a similarly unwalkable strip mall.

Finally, in the sweet spot of moderate density and mixed uses, we find our good friends the tree grates.  Unlike the urban core, there are few skyscrapers here, so enough light pours onto the street to support tree growth.  Unlike a strip mall, the sidewalks are constantly in use by people who prefer the protection from the elements--especially a blistering sun--that trees can provide.  And unlike suburban residential, buildings come right up to the property line, so there isn't any room for a sterile parkway where huge elms and oaks can take root.  The tree grate protects the little slice of nature we allow ourselves in the city, and still affords us a generally un-interrupted sidewalk. 

So how can tree grates be an indicator species when they don't choose where to be of their own volition?  In the same way that planners can design better bicycle infrastructure by asking "what can we do that would bring more women here?" they can similarly ask "what kind of neighborhood should we promote so that a sidewalk dotted with tree grates is the right fit?"

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