KGW.com: "TriMet started Fareless Square in 1975 in response to the federal Clean Air Act. The idea was that offering free public transportation in downtown Portland would cut down on carbon monoxide in Portland.
It worked. In 2008, TriMet said carbon monoxide was no longer a pollution problem in downtown Portland.
TriMet also saw a huge jump in ridership as Portlanders began to adopt a consistent use of public transportation, leading to the city’s status as a center for public transit today."