Scaling Urban Climate Solutions: Lessons from Public Transit Buildup in Mexico

How and under what conditions do urban climate solutions scale? This paper argues that scaling starts with subnational policy experimentation and national policy learning: when policy innovation in a major city inspires policy learning in the central government and the central government subsequently adopts policies that mobilize extra public resources. Policy adoption on its own, however, is insufficient for scaling. Adopted policies must yield desired outcomes. This paper therefore furthermore argues that closing the gap also requires effective guardrail institutions: political institutions that discipline political actors and channel political decision-making towards desired policy outcomes. The argument leverages historical evidence from the buildup of public transit in Mexico. Between 2009 and 2016, eight Mexican cities successfully adopted public transit systems. A fiscal support program drove this outcome. The fiscal support program came about when Mexico’s ministry of finance sought to replicate a public transit innovation in Mexico City in other cities across the country. The program proved effective thanks to a capable chaperone institutions, a process for disciplining public authority, and a mechanism for redistributing public outlays. These findings illustrate the importance of local innovation as a means for uncovering effective urban climate solutions, but also underscores the limits of bottom-up innovation as a mechanism for scaling. Scaling in Mexico was neither sparked by cities nor by the central government alone, but rather by an interaction between the two.