After a long silence here at the Heaviest Corner, I’d like to address Birmingham’s broken street grid. The street grid has been a cross-cultural feature of urban settlements since antiquity. The linear grids of Manhattan and Chicago are iconic in American urbanism, and Birmingham arguably has the best linear grid system in the Southeast. Street and block geometry influence commercial patterns, traffic flows, and the pedestrian experience. Birmingham’s exemplary linear grid system is the backbone of its urban infrastructure. Unfortunately, it has been undermined in some areas by attrition in the form of superblocks and highways. The Google aerials below will endeavor to demonstrate just a few of the places in which the grid system was blocked.
A common criticism of the linear street grid system is that it imposes a rationalistic geometry onto a pre-existing topography without regard to context. This may have been true of some historical street grids that were platted with little regard for the area’s natural systems, like Manhattan for example, but it is not a necessary characteristic of street grids, and matters are no different with many lollipop road designs of suburban developments. Birmingham’s grid system, I would argue, was unusually sensitive to features of local terrain, insofar as any human settlement can be sensitive to its ecological context. For example, the grid system breaks down in Highland Park where the terrain begins to vary and develop hilly features that are not amenable to a grid. Instead of imposing a linear rationality onto the landscape, the streets conform to the natural contours of the terrain.
The grid system, with small city blocks, is inefficient from the perspective of moving vehicular traffic, because cars may have to stop at every intersection (unless they run the lights, as I have often witnessed in Birmingham), particularly when the phasing of traffic signals is poorly timed.
In terms of street geometry, superblocks eliminate intersections, thereby facilitating traffic flows. Small blocks also require more investment in public utilities: every extra intersection requires traffic lights, striping, electrical utilities and stormwater evacuation. Thus, on the surface, the total cost to implement a grid of small, human scale blocks seems higher, though there are certainly hidden costs associated with superblocks, such as the fact that the interiors of large buildings on superblocks are often not accessible to natural light, and therefore demand more electricity to illuminate their interiors. The phenomenological, qualitative effects of superblocks on the urban experience are more resistant to quantification. Although the geometry of the orthogonal grid system facilitates directional wayfinding and enables pedestrianism, it is interesting to observe those with suburban spatial wayfinding skills become lost and overwhelmed in an urban grid, as if our cognitive spatial and wayfinding skills have been “rewired” by sprawling greenfield developments.
Superblocks are a common feature of urban campuses, and UAB is no exception. Superblocks often require large setbacks, which erode the street wall, and large setbacks have been shown to enable both increased traffic volume and speed. When a building hugs the street, the limited setback tends to slow motorists. Many of UAB’s campus buildings have enormous setbacks, as opposed to other urban campuses where university and academic buildings are integrated seamlessly into the urban fabric. Superblocks were also utilized in many public housing projects in a Dickensian program to eliminate alleys that were associated with slums and crime. Ironically, superblocks did just as much to facilitate urban blight as they did to eradicate it. Erdreich’s recent post on the brutalist insularity of the BJCC is an interesting exposition of the ultimate fate of these types of developments that ignore not just the human scale, but the very urban context they’re sited in.
It should come as no surprise that the urban renewal project that spawned UAB occurred at around the same time as the interstate highway, which also precipitated greenfield developments and the decline of previously viable urban neighborhoods. Both I-65 and I-20/59 substantially impeded the connectivity of many of Birmingham’s neighborhoods, partitioning the West End, Norwood, North Birmingham, Woodlawn and East Lake from the City Center. The blue paths indicate where the grid was interrupted as part of the grid’s historical design, particularly at the Railroad Reservation.
In this aerial we can see how the BJCC interrupted several blocks of the grid’s northside.
UAB and the medical district introduced a number of superblocks that interrupted the grid.
Although the railroad reservation is a superblock, it is also a part of the original grid system.
A section of 20-59 carves up West Birmingham, sundering a neighborhood in half and impeding connectivity.
The interrupted street grid is now a permanent feature of Birmingham’s urban fabric. There’s no sense in tearing down the BJCC and restoring the grid, but future planning efforts must preserve a human scale, not an autocentric scale, in order to create memorable and viable urban places.