With Martin Wachs - Director of the University of California Transportation Center, we evaluated the existing methodology for vehicle occupancy measurement. Most state departments of transportation (DOT) conduct vehicle occupancy measurements mainly on freeways, in the morning hours, mostly on Tuesdays-Thursdays, and frequently in one direction only. On the other hand, we argue that changing metropolitan transportation patterns over the last 20 years require that measurements be conducted differently. A higher proportion of trips are non-work related and afternoon trips constitute a higher proportion of all trips. Further, as freeways become congested, major arterials take on greater importance.
To properly assess whether congestion management programs have been effective in increasing vehicle occupancy levels, state DOTs need to randomly sample throughout a region. We developed methodologies for drawing a random sample of locations and for conducting the observations.
Here is a map from the study.