Traffic solutions for greener and cleaner cities

Resumen

Cities world-wide suffer from serious air quality problems and are main contributors to climate change by consuming about two-thirds of the world´s overall energy and emitting an estimated 70% of the world´s Green House Gases (GHG). Road traffic is a major source of GHG emissions and the largest contributor to air pollutant emissions in urban environments. Transport emissions have a varying influence on the urban environment, as GHG and air pollutants have different spatial effects: GHG emissions have a global impact contributing to climate change while air pollutant emissions have a major local impact directly affecting human health. Policy makers can make use of different actions to face these emission problems: implement mechanisms that diminish both the trip length and the need to travel (avoid strategies), promote the modal shift towards public-transport systems or non-motorized transport modes (shift strategies) and enhance the efficiency of the remaining travel activity through a more effective management of transport systems and networks or the improvement of vehicle design and fuel efficiency (improve strategies). While avoid and shift strategies may have a direct impact in reducing both air pollution and GHGs in urban areas, improve strategies could led to important air pollution drawbacks due to e.g. the redistribution of the traffic activity to high-populated areas. This thesis stresses the importance of evaluating transport emission reduction strategies by taking into account the different spatial impacts of emissions. To do so, this thesis evaluates climate change and air pollution co-benefits and trade-offs of two speed management strategies (speed reduction and variable speed limits), two eco-traffic strategies (eco-driving and eco-routing) and the combination of these measures (eco-routing combined first with variable speed limits and second with eco-driving). Three types of methodological tools were applied to model, assess and map the impacts of the measures on traffic performance, traffic emissions and population exposure in Madrid Metropolitan area. A total of 61 scenarios were simulated for different traffic periods and different percentages of penetration of the eco-traffic measures. Results were obtained for six different indicators and up to four types of roads The results show that a speed reduction strategy is efficient to reduce emissions in the section where the measure was implemented. The increase of the operational capacity of the variable speed limit measure led to an increase of emissions in the urban highway where it was applied but a decrease in the city center and in the whole network, showing climate change and air pollution co-benefits. On the other hand, the eco-routing strategy turned out to be positive for climate change mitigation but ineffective to reduce air pollutants in high populated areas. Finally, from the application of the combined measures, perfect environmental and traffic performance synergies were found for eco-routing and eco-driving penetration rates lower than 50% under free-flow traffic conditions. The present study provides local policy makers and city managers with useful tools and insights to achieve greener and cleaner cities through selected traffic management policies.