What (if any) impediments inhibit our ability to answer the question entirely?
There are many complexities to where development occurs, and a great deal of variation in conditions in the region. It can be very difficult to isolate the impact of parking requirements.
The particular analyses using the modeling tools UrbanSim is cutting edge research and, as such, has not been done previously. The development of this model and the data input allows us to quickly generalize findings to a large area; however, results are not meant to be interpreted on smaller scales or for detailed assessments.
Analyzing differences between cities with various parking policies is helpful for a qualitative review of how policies are used by cities. However, there are a variety of factors that influence the characteristics of each city and location, so while this information will be collected, correlations between key indicators and parking demand does not equate to causation.
Private parking is often hard to capture in data collection due to lots that are not directly visible from the street and only accessible via private property. This could hinder data collection to understand discrepancies between actual parking inventory and the parking requirements.