You cannot be well informed about the comparative effect of Critical Mass as against motor vehicles in tieing up the city/obstructing traffic without reading this work by Charles Komanoff.
The site is Right of Way and I've begged the club to donate to it much as it does to TA and R-a-B. Spend time elsewhere on the site to see its work, but you must read this to understand the forces at play as between Critical Mass and drivers.