Bull, O., Muñoz, J. C., & Silva, H. E. (2021). The impact of fare-free public transport on travel behavior: Evidence from a randomized controlled trial. Regional Science and Urban Economics, 86, 103616.
Cats, O., Susilo, Y. O., & Reimal, T. (2017). The prospects of fare-free public transport: Evidence from Tallinn. Transportation, 44(5), 1083–1104.
Fearnley, N. (2013). Free Fares Policies: Impact on Public Transport Mode Share and Other Transport Policy Goals. International Journal of Transportation, 1(1), 75–90.
Kębłowski, W. (2020). Why (not) abolish fares? Exploring the global geography of fare-free public transport. Transportation, 47(6), 2807–2835.
Kȩbłowski, W., Tuvikene, T., Pikner, T., & Jauhiainen, J. S. (2019). Towards an urban political geography of transport: Unpacking the political and scalar dynamics of fare-free public transport in Tallinn, Estonia. Environment and Planning C: Politics and Space, 37(6), 967–984.
Kemmer, L. (2020). Free riding Rio: Protest, political collectives and public transport. City & Society.
Mujcic, R., & Frijters, P. (2020). The Colour of a Free Ride. The Economic Journal, ueaa090.
Philipson, M., & Willis, D. (1990). Free public transport for all? Australian Transport Research Forum, p. 623-640.
Schein, R. (2011). Free transit and social movement infrastructure: Assessing the political potential of Toronto’s nascent free transit campaign. Alternate Routes: A Journal of Critical Social Research, 22, 115–122.
Štraub, D. (2019). Riding without a ticket: Geography of free fare public transport policy in Poland. Urban Development Issues, 64(1), 17–27.
Štraub, D. (2020). The Effects of Fare-Free Public Transport: A Lesson from Frýdek-Místek (Czechia). Sustainability, 12(21), 9111.
Storchmann, K. (2003). Externalities by Automobiles and Fare-Free Transit in Germany — A Paradigm Shift?. Journal of Public Transportation, 6 (4): 89-105.
van Goeverden, C., Rietveld, P., Koelemeijer, J., & Peeters, P. (2006). Subsidies in public transport. European Transport \ Trasporti Europei, 32, 5–25.
Volinski, J. (2012). Implementation and Outcomes of Fare-Free Transit Systems. A Synthesis of Transit Practice. Transport Research Board of the National Academies.
Dellheim, J., & Prince, J. (Eds.). (2018). Free Public Transit And Why We Don’t Pay To Ride Elevators. Black Rose Books.
For academic literature in French, see also the list gathered by.