In the Winter 2013 issue (Vol. 79, No. 1), JAPA published an article by Gregory Pierce and Donald Shoup, “Getting the Prices Right: An Evaluation of Pricing Parking by Demand in San Francisco,” that evaluated the first year of an innovative parking pricing scheme in San Francisco. The program, SFpark, raised and lowered parking prices over time to respond to demonstrated demand for curb parking; the program sought to ensure that parking prices reflected actual demand in ways that reduced cruising for empty spaces. Pierce and Shoup concluded that SFpark had in fact changed driver behavior in the ways sought: It had reduced demand for parking in most treated neighborhoods.
A few months later another set of researchers, Adam Millard-Ball, Rachel Weinberger, and Robert Hampshire, submitted a rejoinder to the Pierce and Shoup article, arguing that the observed differences in parking behavior may have been due not to changes in parking prices, but to relatively random changes in demand for parking, changes having nothing to do with varying prices set by the program. In this context, Millard-Ball et al. also contested the methods Pierce and Shoup had used. I sought five double-blind reviews of the Millard-Ball et al. manuscript and shared that (blinded) manuscript with Pierce and Shoup.
The reviews posed a problem for me. While all of the reviewers felt that Millard-Ball et al. made some valid points, some reviewers suggested that the normal way to respond to such a situation is to write a new article using different methods or data and specifically challenging prior research (and in fact Millard-Ball et al. have subsequently published their own research on SFpark [Millard-Ball, Weinberger, & Hampshire, “Is the Curb 80% Full or 20% Empty? Assessing the Impacts of San Francisco's Parking Experiment,” Transportation Research Part A: Policy and Practice, 2014]). Indeed, the most common way in which our understanding of a variety of planning issues grows and changes is through one set of scholars challenging or building on (and sometimes both) research previously published by other scholars.
I decided in the end to publish both the Millard-Ball et al. rejoinder to the original article and a response from Pierce and Shoup for two major reasons. First, planners are often challenged to prove the efficacy and impact of different planning interventions in a relatively short period of time with limited resources. It seems useful to suggest the potential and the dangers of short-term assessments of any kind of program designed to change people's behaviors in specific ways. Second, and related, the methodological issues under discussion are not particularly sophisticated in themselves; many readers may have used or commissioned or depended on analyses based on such methods. To the extent that is so, it may be helpful to understand the strengths and weakness of such approaches. Finally, I also found both manuscripts to be well written and well argued. I would be interested in reader views on the value of such an exchange, which follows below.