Impact of intersection design on air quality

During the period 2000-2009, the city of Groningen has been restructuring the beltway. The redesigning of the intersections and the impact on urban air quality was the motive for the research conducted. This thesis describes the effects of intersection design on the basis of the emissions of two exhaust gases: nitrogen oxides and particulate matter. High concentrations of these exhaust gases are a threat to human health and the local environment. Therefore, this study tries to answer the question whether intersection design or policy measures can be used to improve the air quality near intersections. The main research question was formulated as follows: What is the optimal policy for designing intersections, from the point of view of exhaust gas emissions over time with varying policy measures and changing mobility demand? To answer this question, several sub questions were formulated concerning transport characteristics, environmental characteristics and policy measures. To tackle the problem of each intersection being unique, one specific intersection was studied in this study. The bottleneck of the beltway of Groningen, Julianaplein, served as the case under consideration. All mobility data used in the model belong to this specific case. A spreadsheet model was developed to calculate the overall emissions of nitrogen oxides and particulate matter near an intersection on an average working day. The model consists of emission factors for three vehicle categories. For these vehicle categories (heavy traffic, buses and light traffic), the average traffic intensity of Groningen on an average working day is inserted in the model for three different time slots to discriminate between quiet moments and rush hour. The results are different traffic loads during the day. The traffic load is also dependent on the capacity of an intersection. Five types of intersection are discussed in this thesis. The capacity is not the only difference between the intersections, because the performance influences the average speed and emissions as well. The performance of an intersection is defined as the percentage of vehicles that can drive according to an ideal speed profile. The rest of the vehicles will drive slower. Two congestion speed profiles were developed to account for the slower vehicles and delay due to the design of an intersection. In general, the model showed that ground level crossings cause more emissions (about thirty percent) than grade separated junctions. The model was also used to assess the importance of the model parameters in the overall impact and the effect of policy measures on the emissions. The environmental characteristics of a vehicle are the main determinant for the overall emissions. Expected emission reductions show the highest potential for improvement, about sixty percent of the current emissions. The traffic intensity is also important, especially the intensity of heavy traffic. The light traffic category has relatively high particulate matter emissions. This leads to the conclusion that NOX emissions could be reduced by nine percent and PM10 emissions by nineteen percent when light traffic would be substituted by buses. Despite some uncertainties in the model approach, the results of this research could be used by policy makers to make well-founded choices for infrastructure projects. Especially for new infrastructure projects, the advice would be to consider grade separated junctions for intersection with high traffic intensity projections. It is a good choice for the air quality, safety and accessibility. For existing infrastructure, the most emission reduction can be achieved by new technologies. Governments should support innovative, cleaner alternatives for existing transport modes and stimulate the car manufacturing sector in the development of these cleaner vehicles.