Microscopic emission modelling

With a focus on the relations between ITS, driving behaviour and vehicle exhaust emissions

Since 1999 the implementation of the new air quality guidelines in the European Union has started. The new guidelines contain fixed limit values concerning the concentration of pollutants in ambient air. In the European member states these developments causes political and social commotion about the seriousness of polluted air people live in. Air quality measurements on several locations through Europe indicate that the concentrations of pollutants frequently exceed the limit values. Poor air quality becomes a serious threat to public health. More appropriate air quality measures should be implemented in order to comply with the European guidelines.

In the urban environment and near the most important national high ways extensive air pollution are measured. At these locations road traffic strongly contributes to the total amount of pollutants in ambient air. To improve the air quality in the urban environment the vehicle emission should be reduced. Because of the oil depended economy a large-scale use of clean vehicles (like electric or hydrogen powered (hybride) vehicles) will not be realised soon. Therefore intelligent traffic measures, which have the force to reduce traffic emissions by influencing driving behaviour, are needed. Traffic dependent traffic lights, DRIP’s and in-car applications, all systems developed to increase road capacity, can be used for environmental improvements too.

The objective of this Master’s Thesis is to develop a modelling method which is capable of assessing vehicle exhaust emissions, including the effects of ITS-measures, on a microscopic level. The method will be designed to forecast the effects of ITS-measures. The assessment of effects (on network performance and air quality) in advance is needed to realise an effective implementation of the ITS-measures.

Several methods used nowadays determine the air quality with a macroscopic link between traffic models and air quality models (based on mean flow and speed). The models are not able to take into account the influence of individual movements of vehicles, like speed variations and complete stops, on the emissions of pollutants. Because of the important influence of individual driving behaviour on emissions the use of microscopic traffic simulations model is preferred. These models simulate the movements of vehicle individual.

The research is divided into four research steps.

Step 1 First of all an analysis of the locations at which one of the limit values is (or more are) exceeded due to a large amount of air pollution will be performed. The results of this analysis can be used with the selection of those ITS-measures that are expected to be effective in reducing the vehicle emissions on these locations. Furthermore a literature study on traffic, emission and air quality models used to determine traffic emissions will be undertaken. The investigation of the quality of the results obtained with these models is a major concern.

Step 2 Empirical data (on-road emission measurements) will be used to formulate relations between driving behaviour and vehicle emissions. The most descriptive characteristics of driving behaviour (i.e. speed or acceleration) and vehicle types (i.e. mass, engine type) will be determined for each pollutant and expressed in model relations. The design of the relations will be depend on practical conditions. The relations should be linked to the available microscopic traffic simulation model VISSIM.

Step 3 The designed modelling method will be tested during a Case Study. Within this study vehicle exhaust emissions will be calculated with and without the implementation of one of the selected ITS-measures. A realistic traffic situation will be modelled. The results will be evaluated with use of a sensitivity and uncertainty analysis. The essence of this research step is to visualise the uncertainties which, due to inevitable inaccurate data, relations and models used, will evolve out of the results. The relevant question is: is possible to justify the effects of the measures with a sufficient degree of significance.

Step 4 The research will be completed with the comparison of the obtained modelling results with the measurement and modelling results of similar researches (collected in the first and second steps described above). With an outline of the strengths and weaknesses of alternative methods the quality and application possibilities of the designed method will be criticised. These findings shape the main results of the research, and will be completed with some methods improvements (the required effort and resources to perform these improvements included) which can be recommended.

The Master’s Thesis is being performed in co-operation with the engineering consultant Witteveen+Bos: