The Evolution of Eco-routing under Population Growth: Evidence from Six U.S. Cities

TL;DR

This study models and analyzes how eco-routing impacts urban emissions and travel behavior amid population growth in six U.S. cities, revealing superlinear emission scaling and the effectiveness of targeted infrastructure upgrades.

Contribution

It introduces new equilibrium models and a comprehensive simulation framework to evaluate long-term eco-routing effects under population growth.

Findings

Eco-routing reduces total emissions but emissions scale superlinearly with population.

Travelers increasingly choose shorter routes, creating carbon bottlenecks.

Targeted capacity expansion at critical bottlenecks reduces emissions by 3% and travel time by 28%.

Abstract

Rapid urban population growth drives car travel demand, increasing transport carbon emissions and posing a critical challenge to sustainable development. Although existing studies have demonstrated that eco-routing can reduce individual emissions, research gaps remain. On the one hand, such personal reductions have a negligible impact on overall emissions, and cannot be simply aggregated to capture the complex effects of large-scale eco-routing. On the other hand, under population growth, the long-term effectiveness of eco-routing, as well as the evolution of its efficiency and traveler route choice, remain underexplored. To address these limitations, this study proposes Time-Only and Time-Carbon user equilibrium (UE) models, integrates them with a demand forecasting method for simulating future network traffic, and designs multi-dimensional metrics to characterize urban dynamics. Using real-world road networks, commuting origin-destination (OD) demand, and population projections under various shared socioeconomic pathways (SSPs) for six representative U.S. cities as a case study, we conduct a comprehensive analysis of urban dynamics across different routing strategies and population sizes. The results reveal that while eco-routing mitigates total emissions, emissions in most cities scale superlinearly with population, a scaling order that remains invariant regardless of routing and construction strategies. Moreover, under population growth, travelers using eco-routing tend to increasingly select shorter routes, giving rise to carbon bottlenecks. A strategy of targeted capacity expansion on these critical bottlenecks (0.46% of links) significantly reduces both emissions (3%) and travel time (28%) without compromising eco-routing efficiency. This study provides a foundation for formulating low-carbon urban transport planning and emission reduction policies.