A more valid design would be randomly assigning some cities to institute congestion pricing, and other cities to not have it. Obviously not feasible in practice, but that's at least the kind of thing to strive toward when designing these kinds of studies.
Cities are stupidly heterogenous. These data wouldn't be more meaningful than comparing cities with congestion pricing to those without. (And comparing them from their congestion eras.)
"Our treatment units are stupidly heterogeneous" is exactly the problem it solves. A century's worth of developing increasingly sophisticated statistical techniques for making do without random assignment has thus far failed to accomplish anything than provisional mitigations that are notoriously easy to use incorrectly in practice.