Urban congestion relief experiments through routing-app interventions

Traffic congestion remains a persistent challenge for urban mobility, increasing travel delays and elevating CO 2 emissions. The widespread use of smartphones and GPS navigation creates new opportunities to mitigate congestion through routing optimizations in apps, yet real-world evidence for the effectiveness of such interventions is limited. Here we report large-scale empirical experiments evaluating routing-based traffic interventions on ~100 highly congested road segments across 10 major US cities. By rerouting a small share of Google Maps trips from targeted congested highway and arterial segments to less congested alternatives of equivalent road-classes with comparable travel times, we observe a city-average 2% increase in vehicle speeds on the intervened segments, along with improved travel times 0.7% and potential annual reductions exceeding 1,000 tons of CO 2 -equivalent emissions per city in the majority of studied locations. These findings provide evidence that marginal routing interventions involving a small proportion of vehicles can measurably enhance overall road network efficiency, offering a practical pathway to easing congestion and advancing urban sustainability.