Urban Planning 101 – Block Size

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A few of our recent projects have spanned the length, or width of an entire city block. That got us thinking about the urban grid, how it lays out and why some blocks are bigger than others. Now, you’ve probably never measured your city block. We we’rent even sure how at first. But one thing is for sure; block size does matter. Although large or small does not mean good and bad.

The general thinking since the Jane Jacob’s brought the concept of urbanism to light in the 60’s has been that, unlike many other scenarios, the smaller blocks have the advantage. Smaller blocks allow more variation in your daily commute and spread out the foot traffic around a city. It also provides a city more intersections which are always ideal places for commercial activity. The end result is a more walk able city and more unique shops and restaurants.  Good stuff.

We wanted to apply this thinking to Philadelphia and see how our block sizes influence the health of our urban streets. Our work analyzing potential properties over the years has certainly helped us get familiar with block sizes in Philadelphia, familiar enough to notice they are not at all uniform.  The center city laid out by Billy Penn is a pretty typical grid, but since then streets have been added and cut up. More often than you’d think. There’s Sansom in between Walnut and Chestnut and Hope street in Kensington. Or Ionic which runs for a block in center city stops for 3, then runs for two more then stops again. Then there is Corinthian in Fairmount and Frankford Ave. in Fishtown.  We felt like beginners way over our heads trying to figure out what block sizes meant in Philly.

So we shelved the Philly idea for now and looked to New York and Portland instead. New York always has tons of information about its urban structure thanks to Jane Jacobs and Portland has a cool TV show so we figured what the hell.

New York


Jane Jacobs argues that the long blocks of Manhattan do it a disservice. Manhattan’s streets and Avenues measure 200′ x 900′ from center of street to center of street. It makes walking cross town seem like an arduous task because it takes forever to reach the next block while uptown or downtown seems to pass by more quickly. Although this block setup works well for navigating the island Jane suggests that it restricts the location for business and stratifies building uses. Business can’t succeed on the streets because few pedestrians walk down them and they flourish on the avenues because of the outpouring of people. With the value of mixed building use we have come to understand (see Urban Planning 101 on mixed use) we would agree with Jane here.

Portland


Portland is a different animal. It’s blocks measure 200′ x 200′. Actually the smallest block size in the country. With the recent urban success of Portland and Jane Jacob’s analysis of cities the point is almost proven that small blocks are better. If Portlandia does the city any justice then  a variety of paths to walk down area a good base for a mixed use neighborhoods with hip organic restaurants, a feminist bookstore and maybe even a “Bad Art Good Walls” if you’re lucky.

Ultimately what Jane Jacobs and Portlandia are telling us is that if the pedestrian activity on the streets is spread out and unpredictable, building uses can also be spread out and unpredictable. Makes sense.

But there is more to block size than the flow of pedestrian traffic and its effects on building usage. Having smaller blocks means having more streets. Having more streets means having fewer buildings per square mile, which means a lower density overall, which means less capital being exchanged and which means the value of city land is lower per square mile. You could make up for that by building huge skyscrapers on small blocks but even that has its limits.

But that’s not all! Smaller block sizes also means giving more land over to cars, to infrastructure that has to be maintained and to a more extensive stormwater management challenge.  So although small blocks do have their benefits, I think a lot of people prefer them big. Portland may be in a fit of success now but it certainly took some time to get into the lime light while New York’s density has been upholding that city for a long time.

Philadelphia

It was a great learning experience to think about these two cities. But we live and work in Philadelphia. We still want to know how our block size sizes up. So back to the drawing board. We started in Center City, this is a view of the streets around Rittenhouse square. Some regular block sizes do emerge if you can ignore all the small one lane streets and alleys.

Next we tried Fishtown because our block to block Awesometown project has gotten us looking at the street network a lot over there. Turns out it actually has a less broken up grid than Center City but still with varying block sizes. Not to mention a different orientation.

Finally South Philly, Where we found our most regular block size, again ignoring alley ways.

After some long staring at each image the grid starts to emerge and a few regular block sizes come out of that. All in all 450′ x450′ is the most common. But that is if you can ignore the small side streets and alleyways. I’m not sure if you’re allowed.

But ignoring them for now we can analyze the results of our block measuring competition. Philadelphia is larger than Portland in length and width, larger than NY in width, smaller in the length.  In total block area Philly is actually larger than NY (180,000 SF to 202,500 SF).Of course all of that is ignoring alley ways. With alley ways we are a city comparable to Portland in block size and number of intersections, although with the potential in a few non-broken up blocks for higher density. It sounds like we have a nice variety which plays in well with the need for mixed usage. The square blocks, (or smaller rectangles if you count alley ways) makes our city less striated than New York’s streets vs. avenues.

All in all we feel like we came to some understandings of how block size impacts a city, but we still aren’t sure what to do with the alley ways. Philadelphia is almost like a free for all with the occasional major border vacuums dividing the city into neighborhoods. Thank god we didn’t look at medieval streets.

It feels like we’ve got some more theorizing to do on how our broken up grid affects us and what the alleys ways really do, if anything for our city. For now we’d have to estimate that our block sizes keep our city a field of varying activity with a few major streets to differentiate neighborhoods. Think you have a better idea? Well tell us in the comments.

 

One Comment

  1. Bill Marston says:

    Lengths of the sides of blocks does have significance on both street character and overall urban density (of land vs. street in particular, but of course that directly tips the amount of hard-surface vs potentially absorptive surface regarding solar heat gain, stormwater management, vegetation content as well).

    Your verbal exploration clearly does not address urban form and thus development character of these widely different block sizes either. Surely this was also beyond the scope intent of your article, but is of vital interest to both developer and resident.

    Picture, for example, a larger uninterrupted footprint potential that the Philly pattern shows. It could mean a much smaller percentage of “eyes on the street” and its impact on community sensibility, and sense of safety.

    Or look at the potential to redistribute open vs. built portions of a more massive Philly block. One can picture a firm built edge at the main street faces but a far more flexible design within.

    I recall visiting, some 40 years ago, as a brand-new renter here, the interior of a block between society hill and queen village. The rowhouse homeowners had substantially aggregated their back yards into a large shared community garden & recreational area. I have no idea what form of structured provisions those neighbors had developed but somehow it was working for them. That block was bounded by fairly long dimensions in both X and Y directions, yielding a common space of substantial size that did not impinge upon the back walls, windows & doors of the surrounding houses.

    This might serve as a minor example of such a policy-potential in re: vacating of ROW for internal alleys & minor streets where a major street-free land development area can be created. Surely there are numerous examples in our big old city, so it isn’t really a new thought — just another factor on this topic. Thanks, Chad.

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