Comparative environmental evaluation of highway speed limit strategies: a microsimulation study.

Speed management policies are cost-effective tools for mitigating traffic emissions, yet comparative studies remain fragmented. This study addresses this gap through a novel framework comparing three highway speed limit strategies, Uniform Speed Limit (USL), Differential Speed Limit (DSL), and Lane-Based Speed Limit (LBSL), using microsimulation-based elasticity analysis across 432 scenarios. Contributions include: (1) the first comprehensive multi-pollutant comparison under controlled conditions; (2) a systematically compared framework demonstrating log models' superiority for emission prediction; (3) quantified interaction effects showing elastic responses to traffic volume but inelastic responses to speed changes; and (4) a comparative framework that offers qualitative guidance for policy in contexts characterized by heterogeneous vehicle fleets. Results show LBSL significantly increases emissions relative to DSL (NOx +46.8%, CO₂ +28%), while USL presents trade-offs (CO - 7.6%, but NOx +14.7%). DSL demonstrates the most favorable relative environmental performance under the tested scenarios. Findings emphasize that effective policy must simultaneously consider traffic demand elasticity, speed regimes, and fleet composition rather than uniform approaches.