Environmental traffic restrictions are increasingly implemented in cities. One popular strategy consists of setting up Low Emission Zones (LEZs) that regulate or restrict the access to a dedicated urban area, for different classes of polluting vehicles. While LEZs are growing in numbers, there is a lack of objective evidence on when and how they actually contribute to reducing air pollution.
The main objective of a paper by Virginie Lurkin et. al. is to show how different LEZ setups lead to different impacts on air pollution. The researchers use a conceptual framework based on simulated traffic data and behavioral hypotheses allowing decision-makers to investigate easily a wide range of scenarios including different assumptions related to the Vehicle, Area, and Time dimensions of the LEZ, as well as the behaviors of road users. The analysis highlights that increasing the severity of the operational rules does not necessarily lead to the intended emissions gains. A major reason lies in the negative spillovers associated with the undesired behaviors of road users (e.g., drivers deciding to take detours and drive around the forbidden area). Therefore, there is a need to consider carefully those aspects before establishing the LEZ.
These conclusions impact several policy implications. First, decision-makers should invest sufficiently early in scenario-based analyses before the establishment of any LEZ, with the goal to grasp the interactions between VAT dimensions and behaviors of road users. Second, in order to include realistic behavioral assumptions in their analyses, decision-makers should collect comprehensive data documenting behaviors or revealed-behaviors of vehicle users when facing a LEZ. Third, decision-makers should consider including several real case studies in their analyses, in close collaborations with cities. This would allow them to use real traffic data, retrieving the essential characteristics of the trips (i.e. the origin, destination, travel distance, speed, and departure time of individual trips), thus going beyond conceptual analyses.
A single policy instrument can rarely serve as a standalone solution to complex environmental and societal challenges, such as reducing urban air pollution. Therefore, next to banning polluting vehicles to enter specific areas, policymakers should also consider other measures of emission reductions, e.g. road pricing, and investigate the mutual interactions they have with the implementation of a LEZ.
Source: Virginie Lurkin, Julien Hambuckers, Tom van Woensel, Urban low emissions zones: A behavioral operations management perspective, Transportation Research Part A: Policy and Practice, Volume 144, 2021