Assessing Dynamic Traffic Management Used to Reduce Greenhouse Gases Emissions and Pollutants
GADRAT Marie, Cerema, South West Territorial Division, HERVE Aurelie, Cerema, South West Territorial Division
Stakeholders from Toulouse are in the process of revising the plan that fix objectives and measures in order to protect the atmosphere. This paper is about an ongoing study conducted to mitigate GHG and pollutants in the vicinity of urban motorway.
Summary. Stakeholders from Toulouse urban area are in the process of revising the plan that fix objectives and measures in order to protect the atmosphere. This paper is about an ongoing study that is being conducted to mitigate emissions of greenhouse gases and pollutants in the vicinity of Toulouse urban motorway.
It pays particular attention to the modelling in 2020 of GHG and pollutants of light vehicles on the motorway in three specific scenarios: no traffic management, dynamic speed management, dynamic access management.
First, the paper presents the context of the study. Then, we will see traffic management strategies evaluated for the purposes of the PPA and how they are simulated (dynamic traffic simulation). And finally, methods for the calculation of greenhouse gas emissions and pollutants will be discussed. This last point is the heart of the article.
Context of study. Toulouse is a very dynamic city in the South West of France with more than 1 250 000 inhabitants (demographic growth +6,8% in the last 5 years). There are some congestion problems mostly during peak hours. And air quality is not quite in the regulatory prescribed limits. To face such issues, many stakeholders in the area – State representatives (Préfet, DREAL Midi Pyrénées, DDT 31), the metropolitan authority (CUTM), the urban transit authority (Tisséo), Regional observatory of air quality (ORAMIP)... – are working on strategies to protect the atmosphere.
The atmosphere protection plans (PPA) is a regulatory document that defines the objectives and measures to bring inside agglomerations of more than 250 000 inhabitants and areas where regulatory limits are exceeded or are likely to be, the concentrations of pollutants to a level below the prescribed limits. Like most planning document it is the result of a long process with many stakeholders involved. The final document has three parts: a diagnosis, the list of objectives and then the proposed measures to mitigate GHG and pollutants.
In the last PPA of Toulouse, modelling of air pollution at 2015 showed that the proposed measures to improve the air quality was not sufficient enough. Indeed, more than 10 000 people will still be in areas where air pollution would be beyond the regulatory limits. The majority of those people is near high traffic routes including the Toulouse ring road.
Traffic management strategies to mitigate emissions. As part of the review of the PPA, the modelling of pollutant concentrations is updated to the year of 2020. Although a number of mitigation measures were implemented in the model (demand travel modelling and air pollution modelling), the results still show an unacceptable number of people with bad air quality conditions. Thus, it was decided to provide one generic measure in the PPA that will set the goal of emission reductions to be achieved. It is the measure B8: "Implementing additional measures to reduce emissions from traffic on the Toulouse area". The strategies identified in order to achieve this goal are dynamic speed control during peak hours on Toulouse west ring road and dynamic on-ramp metering during rush hours.
The impact on emissions of pollutants and greenhouse gases of these two traffic management strategies are evaluated in this study.
Effects on traffic flow. Effects on traffic flow is studied using a dynamic simulation model, more appropriate to assess the impact of this type of measure. The tool used is an experimental platform for simulation at the mesoscopic scale. It takes into account the latest research on the effects of dynamic traffic management such as speed and access control. Vehicles included in this study are light vehicles only.
Models for estimating emissions from light vehicles. Emissions of pollutants and greenhouse gases are calculated with HBEFA (Handbook Emission Factor for road transport). HBEFA is based on a traffic situation approach to take into account the dynamic of traffic. A traffic situation is the combination of zone description (urban or rural), type of road (highway, ramp, distribution road, etc.), speed limit and 4 levels of service: freeflow, heavy, saturated and stop and go.Levels of service are determined by 6 minutes interval depending on flow and speed data. Those data are the results of traffic simulation. For each tratfic management strategie, emissions are calculated and compared with the situation without traffic management to determine the gain in quantity of pollutants and percentage due to this measure.
The article will mostly develop the last part of the study focusing on estimating emissions from dynamic trafic management.
Association for European Transport