According to his blog, HumanTransit.org, Jarrett Walker has been a full-time consultant since 1991.
This quote is taken from a "conversation about expertise vs. activism" between Walker and an engineer named "Scotty" (From HumanTransit.org):
"Reputable consultants ought not take work that involves declaring that night is day, in an attempt to paper over a blatantly bad political decision. However, in situations like just described, there is plenty of work for reputable consultants to help transit agencies to make the best of a bad situation--if the political realities of a situation require that agency A implement a transit network using only mixed-traffic streetcar, and that other modes are off the table, a good consultant will help them design the best streetcar system that lies within their budget."
Scotty: "Often times the "values" in question aren't the values of the riders, the community, or the sponsoring agency, but those of the powerbrokers who ultimately control the fate of the project in question."