On the relationship of speed limit and CO2 emissions in urban traffic

Abstract

The paper analyzes the relationship between urban speed limits and vehicle emissions. There is an ongoing trend of reducing speed limits from $50\mathrm{km/h}$ to $30\mathrm{km/h}$ for the sake of increasing road safety. However, the impact of this policy on ${\mathrm{CO}}_2$ emissions is still unclear. It can be mixed depending on the proportion of dynamic and steady-state driving. While cruising emissions are higher at lower speeds, lower speeds entail less acceleration in urban traffic. Based on our investigation, one network topology feature (road length) and two traffic-related parameters (traffic volume and turning ratio) have been suggested for analysis being the most relevant to affect vehicle emission. Their correlation with potential emission reduction was evaluated using high-fidelity traffic simulation based on traffic scenarios validated with real traffic data. Random forest regression was used to support the optimal selection of zones for speed limit reduction. Traffic simulations on large urban networks prove that ${\mathrm{CO}}_2$ emission reductions of over 10% can be achieved in the case of a well-chosen speed limit policy.