Here is a blogger who has done hard work to collect statistics on paying for transportation

https://reports.mysidewalk.com/bfb9734ce2

Thorough academic study of fare-free public transport

Although the policy of abolishing fares in public transport—here referred to as “fare-free public transport” (FFPT)—exists in nearly 100 localities worldwide, it has not been thoroughly researched. To start filling this gap, I enhance the conceptual clarity about fare abolition...

...I offer the most comprehensive inventory of full FFPT programmes to date

...Supported and contested by diverse rationales, it cannot be analysed as transport instrument alone.

https://link.springer.com/article/10.1007%2Fs11116-019-09986-6 

Environment key reason for fare-free public transport

First, the Environment set of goals represents the key reasons that initiated the creation of FFPT and they continue to be the main motivation for promoting this concept. Such a range of goals covers issues, which are closely tied to car-use externalities, for example, car accidents, traffic congestion, air and noise pollution, and the increasing dependency on cars. By abolishing fares, the municipalities are trying to encourage people, especially car drivers, to use public transport instead of cars (Storchmann, 2003; De Witte et al., 008; Zhou, Schweitzer, 2011; Cats et al., 2017).

http://humangeographies.org.ro/articles/131/a_131_3_straub.pdf 

Thorough study of fare-free public transportation

Free urban transit is a growing trend. In 2016, there were no less than 107 entirely fare-free public transport networks around the world, including over 30 just in France (CGTPAG 2016; Keblowski 2016).

https://www.metropolitiques.eu/Dunkirk-as-a-New-Laboratory-for-Free-Transit.html

Worcester, MA, case for fare-free public transit

Public transportation is treated differently. The Worcester Regional Transit Authority charges most adults $1.75 per trip to board the bus, a disincentive to make use of what could be a cornerstone of the region’s transportation network. Ridership is dropping, declining 23 percent between 2016—before the latest fare hike—and 2018. Last year had the fewest passenger trips since a driver strike in 2005, and the lowest in a non-strike year since tracking began in 1991.

http://www.wrrb.org/wp-content/uploads/2019/05/WRRB-FareFree-Transit-Report.pdf