We devise a difference-in-difference study design to assess the impact of fare-free bus service in Alexandria, located in the Washington, DC metro area. Our surveys show modest to no effect, with at most 6% more residents in Alexandria increasing their bus usage compared to control locations. We find no effect on ground-level ozone or road crashes, suggesting little to no impact on road traffic. One-third of respondents in control locations indicated they would use buses more frequently if fare-free service were available in their areas. Based on the respondent-reported reductions in car miles, the program led to a reduction of 0.294 to 0.494 tons of CO2 per year, or 5% to 9% of the average annual emissions from a US car, at a cost of 70−120 per ton of CO2. We predict a CO2 reduction of 0.454 tons per year, equivalent to 8% of the average US car's annual emissions if the fare-free bus covered all of the study areas.
@article{arxiv.2601.02190,
title = {Fare-Free Bus Service and CO2 Reductions: Evidence from a Natural Experiment},
author = {Anna Alberini and Javier Bas and Cinzia Cirillo},
journal= {arXiv preprint arXiv:2601.02190},
year = {2026}
}