Last spring, I heard about an interesting dataset about Ann Arbor, Michigan, where I lived for four years as an undergraduate student. Busy with the flurry of activity leading up to my completion of graduate school, I stored it away to look at later. After all, real-time information on cities is hard enough to come by, let alone on the simultaneously ubiquitous and fascinating topic of parking.
The parking lots and structures in downtown Ann Arbor are operated by a quasi-public organization, the Ann Arbor Downtown Development Authority (DDA). Together with their parking vendor, last April they implemented a system that provides real-time information about the number of parking spaces available in several lots and garages through digital signs at each garage and through their website. An old Ann Arbor friend Brian Kerr wrote a simple script to scrape that page every 20 minutes and record the number of spaces available at each facility. After letting it run for about two weeks, he posted the data file online. Subsequently a local blogger interviewed the DDA’s IT manager about how the system was implemented, and even posted some charts encouraging visitors to match the chart with the garage. The data sparked a bit of interest on local blogs but the conversation soon died out.
At the time of the completion of a recent parking study in 2007, the DDA operated lots and structures containing 5,770 parking spaces in downtown Ann Arbor. These facilities are concentrated in a relatively small physical area, as shown in this map from the study:
For my first pass at the data I thought I’d look at just one garage, indicated by the arrow above. As is shown, the Maynard Street structure is near two movie theaters, a busy commercial district, and one block from the University of Michigan Central Campus Diag, with many classroom buildings and a large auditorium. The first chart is the number of spaces available in just one day – Monday, April 7, 2008:
The first thing to notice is that the garage is never full during any 20-minute measurement. Although the technical capacity of the garage is 797, the garage flat-lines at 618 (perhaps due to long-term permits or construction). The garage is only filled over 90% of this reduced capacity for one 40-minute period, from 1:40 p.m. to 2:20 p.m, or roughly 2.7% of the entire 24-hour period.
Expanding the time frame for the next 7 consecutive days reveals this pattern:
The spikes correspond with the midday rush, and the garage only fills once, around 1:00 p.m. on Friday, April 11th. This seemingly dry data can tell a rich sociological story; everyone rushes in just after nine, with various people lingering around into long into the evening. In a sense, the curve represents a unique DNA of the local land uses and the preferences and customs of their auto-using patrons, residents, and visitors.
Based on the data we can make a couple observations. First, the vast majority of the parking lots and structures are almost totally empty the majority of the time. This means they represent a huge amount of inactive urban space. A common rule of thumb is each structured space takes up 300 square feet of floor space for the bay and associated aisles and ramps. If we use this standard, the same floor area in this garage could be 239 apartments (assuming they average a generous 1,000 square feet). Certainly good design would demand a residential structure be taller or configured differently on the site. However, given the extremely fickle use of the garage now, a residential use would mean more people physically at the site on average than are now.
Second, from the chart above we can see that parking demand at the DDA’s prevailing price structure is very spiky, with extremely high demand only at limited times. (This garage costs $.80 an hour, or $175 for a monthly permit) It would seem logical for the DDA to use variable or tiered pricing to create a market incentive for a more efficient use of their space. For example, parking overnight could be inexpensive given the very low demand, with parking around the midday peak much more expensive. Even a modest form of performance parking may change this observed pattern.
Despite nearly 5,800 spaces the DDA continues to develop more parking, this October publishing on their website details about a proposed underground lot near the library boasting green design. How will the city know when they have enough parking? After all, parking policy guru Donald Shoup points out one can rarely provide enough of something that’s under priced. The proposal for the new garage advises readers to “review the findings of the 2007 Parking Study to learn why vehicle parking is needed even with extensive investment in alternative transportation.” Unfortunately the 2007 Parking Study doesn’t exactly settle the matter, including as one of its final recommendations “Maintain a formalized process for determining when new supply is needed.” The study, by the alternative transportation experts Nelson/Nygaard, is chock full of state-of-the-art policy suggestions (including variable pricing discussed above) but avoids the sticky question of determining how much is necessary. Perhaps it’s because like other seemingly scientific questions in urban planning the answer is not scientific but value-laden and political. (A similar question: How many freeways and/or lanes do we need?) And in Ann Arbor, the people want more parking.
Parking in the Real-Time City
In another vein, publishing this real-time data (especially on a still forthcoming mobile format) could itself have profound implications for the transportation system. Could real-time data allow people to avoid full structures and make use of the resource more efficient? The Washington, D.C. suburban rail station lots tend to fill up early, and I’ve heard stories of people driving downtown stopping at each station to look for a spot. What if the space was beamed to their home computer or car? (The more important question might be, “How much parking should they provide to begin with, and what should it be priced?” One suggestive study I saw of San Francisco’s BART concluded replacing parking with offices would boost the agency’s riders and revenue) If the DDA makes summary data available on the website, it would make costly data collection unnecessary for this data point. All citizens would know exactly how full or empty the garages were, and the DDA would be able to observe the impact of pricing or policy changes in real time.
> Previous parking posts: The Urbanists’ Panacea: Parking Reform, Are Expensive Parking Meters Fair?, more
> Homeless Dave’s Interview with the DDA’s Stephen Smith
> Ann Arbor Downtown Development Authority