Across urban and metropolitan regions worldwide, developing a new transit system is often considered an effective way to address traffic congestion. The Jakarta Mass Rapid Transit (MRT), the first subway system in Indonesia, aims to achieve that goal. Using a before-after, treatment-control evaluation design, we estimate the impact of the MRT Jakarta on corridor-level congestion using data derived from Google Maps and accessed through its application program interface. Results from difference-in-differences regressions indicate a considerably modest and largely localized short-term congestion reduction impact where improved roadway performance was observed mainly along the city’s central business district corridor.