On the one hand, it seems like studying a situation before you try to regulate it is just common sense. And that's what other, more professional, planning departments elsewhere have done. See the examples below for the kinds of data that NYC and Portland collected and analyzed before proposing changes to their parking requirements.
But that's not what DC's Office of Planning did. Instead, at the beginning of the ZRR, OP commissioned a very different kind of study. Here is the consultants' account of what they were asked to do:
The project’s Kickoff meeting established that the project was initiated out of a perceived need to update the District’s zoning requirements, many of which were felt to be too accommodating of personal vehicle travel given current transportation opportunities (high-level transit service, increased transit-oriented and mixed-use, high-density development) and constraints (regional and local roadway congestion). While noting potentially strong opposition from some stakeholders, it was concluded that the primary goal of the current project was to identify zoning changes that would result in reduced accommodation of parking at new development in the District.
In other words, the ZRR started from the premise that the goal was to increase parking scarcity -- not to right-size parking. So we got an ideologically-driven set of proposals rather than an empirically-grounded attempt at problem-solving.
It's time to go back and do it right. Study first, then propose changes.
The studies below are interesting not only for their substantive conclusions, but also as potential models for research design on this issue.
Manhattan Core Public Parking Study
Residential Parking Study
Inner-Ring Residential Parking Study (this December 2013 report is my weekend reading)
Parking Impacts for New TOD along Portland Inner Corridors