Monday, September 7, 2009

The Invisible Signs of Savannah

The Odonomy of Savannah II: The Case of the Invisible Signs

Savannah is well loved by this blogger for its active street frontage, its romantic buildings, its strangely abundant rows of townhouses (strange, that is, here in the South), its demure and pleasant gardens, and those redolent live oaks making the streets of the city beloved, well-shaded and well-lived. But among the things that I love about Savannah the most is what it doesn't have. Thanks Carfree and Eli for pointing out some missing items that should draw more attention to the elegance if Savannah's fine-grained street grid: the strange scarcity of stop signs and signalized intersections in this city.

To draw out my point better, I've decided to compare the First Ward of Charlotte, which has a typical downtown grid, with an equivalent area in the Historic District of Savannah. (Much of First Ward was formerly the Earle Village projects of the Charlotte Housing Authority, which is a well-known, early '90's Hope VI redevelopment that was among the first - and very successful - introductions of New Urbanism to Charlotte.) Below are images of the block pattern of First Ward and of Savannah's Historic District, each showing an area of exactly 1/4 square miles:



I should first mention that the street areas depicted in white above are the public rights-of-way only (I don't include internal drives). In the case of First Ward, I decided to include the present and future light rail right-of-way (which is part of the "transportation grid" and also creates/will create signalized intersections in the transportation grid; it is the north-south right-of-way corridor furthest to the left).

Charlotte's First Ward is relatively well-connected in terms of street connectivity and represents about the best we can hope for in most southern cities. With more development coming, the large meaty blocks (many are still surface parking lots) represent a lot of future revenue for our city. There are also only 40 intersections in the First Ward study area--much, much less intersections to control or maintain than Savannah. Savannah's study area, in contrast, has a whopping 203 intersections, more than five times First Ward's! But here is one surprise. First Ward has 16 signalized intersections (40% of its total intersections), while Savannah, in all that arabesque madness, only has 13 such intersections (6.5% of the total; these are located along the main east-west boulevards of Broughton, Oglethorpe and Liberty streets). Using Google Streetview I've counted all the intersection types for each study area. Here is the breakdown totals of intersection types for your reference:

Charlotte First Ward Intersections:
1 (2.5%) with a roundabout
16 (40%) with signalized stops
23 (57.5%) with at least one stop sign
40 Total Intersections

Savannah Historic District Intersections:
13 (6.5%) with signalized stops
51 (25%) with at least one stop sign
66 (32.5%) with only a yield sign
73 (36%) with no stop/yield signal or sign at all
203 Total Intersections

The majority, over two-thirds, of Savannah's public right-of-way intersections contain a yield sign or no sign at all. I wonder if such a remarkable feature can even be contemplated by Charlottean planners. Yes, the number above is right, folks, 36% of the Savannah Historic District public right-of-way intersections have no sign controlling intersection traffic! These "implicit yields" are controlled by the environment itself. Intuitively, we all recognize that a narrow and constricted entrance to an intersection with a wider street is a "stop" or "yield"--even if we don't see a sign. Everybody understands that the intersection of an alley with a street represents an implicit stop, just as everybody understands that you don't need a stop/yield sign at the end of your driveway. Savannah knows this and allows the intimate scales of its fine-grain environment to dictate traffic control. In reality, most of the yield signs are not really needed at all, much like yield signs are not really necessary for roundabouts. Traffic engineers just seem to want them there for liability reasons, but, so long as one understands the direction of traffic flow, Savannah's grid is so driver intuitive, that I'm probably right in saying that most drivers do not even register or think about the yield signage as they meander through the city grid.


CarFree Stupidity said...

Ever since finding your blog through Discovering Urbanism I am finding one of my more enjoyable reads.

I just posted about my city's new roundabout, and would like your comments on the design and signage issues.


Thanks and keep up the good work.

Daniel Nairn said...

I paid a visit to Savannah a few months ago and absolutely loved it. I hadn't paid attention to the intersections, but your findings do make a lot of sense. It's like a whole traffic calming district. I wonder what there accident/injury rates are. I bet they are lower than places with more signalized intersections, but that's just a hunch.