The challenges of determing parking demand

Mary S. Smith is a senior vice president and director of functional design for Indianapolis, Indiana-based Walker Parking Consultants. She is also team leader and principle author of "Shared Parking, Second Edition". I was recently on a panel discussion with her where she spoke about the book. She has also recently written an article in the August 2008 Issue of Urban Land magazine. I was very intrigued by what Mary had to say and write because as a parking consultant, I rely on the "Shared Parking" book and accompanying model to determine parking demand for my clients.

I have often asked my self “how reliable is the standard parking model?” Mary indicates that this issue is very complex. She starts out talking about the challenge of determining demand patterns. She explains that there are many factors that affect demand over time that can not be determined prior to a development being constructed. These include knowing the strengths of the tenants, market forces in the surrounding area, and the mix of tenants at a particular location. As an example, she uses the popularity of restaurant or retail stores, which wax and wane over time. Also, office building tenants change over time, with low employee density law firms being replaced by high density telemarketing firms.

Next Mary spends a great deal of time talking about parking demand (how many spaces should be provided) and how to determine the appropriate parking demand for a particular use and or mix of uses. The bottom line is that this is an even more complex issue than determining demand patterns. However, the industry has settled on an approach that relies on determining a “design day” and adding “effective supply,” then making adjustments for paid parking, mode split and internal capture rates (no one yet has determined what those numbers should be either). I know this does not mean anything to the lay person, but the final conclusion is:

"The Shared Parking model is not intended to be a highly reliable predictor of parking demand at any particular location on a particular day, but rather the recommended number of spaces that should be provided based on a relatively (but not excessively) high standard of care to avoid negative impact on the success of the project."

In other words, the parking demand model will result in enough parking not to get you in trouble but probably more parking than you actually need.
As you can imagine, this conclusion has led to considerable controversy due to the fact that it still leads to some degree of oversupply. Donald Shoup who wrote the "High Cost of Free Parking" has had a lot to say about this.

More about that in my next post.