Environmental effects of improved public transport in Groningen

Groningen is a compact city and many people travel every day to the city for work, studies or facilities. This results in a lot of traffic. The municipality has taken measures to limit unnecessary car traffic in the city centre, but this results in a relatively high bus use. All urban and regional bus lines halt directly in or near the city centre. This affects the liveability of the city centre negatively. Due to future economic and demographic developments traffic will grow. If no measures are taken, the problems, caused by traffic, will increase: increasing traffic congestions and stagnation, increasing air pollution and increasing noise nuisance. In order to tackle these problems, the regional government developed a plan to improve city-regional public transport (CRPT), named the Kolibri-PublicTransport (PT)-Network. One of the proposals is the introduction of trams in the city of Groningen in order to limit the amount of bus traffic and to improve liveability. The present research focused on local air pollution. This is a growing problem, especially in densely populated and compact cities with a lot of traffic, such as Groningen. We studied the effect of the PT-improvements on the future emissions of four local air pollutants: NOx, PM, VOC, and SO¬2. This resulted in the following main research question: ‘How will the proposed improved PT for the city of Groningen affect the emissions of local air pollutants?’ To answer this question, the following sub questions need to be addressed: What is the current mobility demand in the city of Groningen and how will this evolve in the future? How do the proposed PT-improvements influence transport mode choices of people and the resulting modal split (MS) in the future? What are the impacts of the studied transport modes (car and PT, now and in the future) on emissions of the four local air pollutants studied? The model we developed to estimate the impact of improved PT on future emissions in the city of Groningen, consists of some uncertain aspects, due to a lack of information about specific aspects in the literature and due to the fact that the model studied future developments. In order to study the effect of these uncertainties on the emissions, a scenario approach was applied, with different variants for all the aspects studied. The emission effects of these variants are compared to a basic scenario, so we were able to assess the relative importance of the different uncertain aspects. According to our model, an emission reduction of around 50 % is expected by 2020, due to expected technological improvements of different transport modes, compared to the current situation. According to our model, the implementation of Kolibri will result in an extra 10 % total emission reduction of all air pollutants studied. People’s transport mode choices were based on the attractiveness of the different transport modes studied. The attractiveness score was used to determine the modal split. To get an idea about the robustness of the model, the attractiveness was varied, and the effects of these variations on the four emissions were assessed. The different applied attractiveness variants had only small impacts on emissions. This result implies that our model is quite robust. Of the four, other uncertain model aspects, on which the scenario approach was applied, one was found to have a relative large impact on future emissions: the rate of future improvement of all transport modes. Extra improvement in the future shows large emission decreases (40 to 45 %), compared to the basic scenario. Less future improvement results in large emission increases (80 to 180 %), compared to the basic scenario. The other three uncertain aspects had about the same, but a smaller impact: future mobility demand increase, changed PT-characteristics, and the future share of trams. A lower future increase results in fewer emissions (decreased by about 12 %), compared to the basic scenario. A stronger increase in mobility demand results in more emissions (increased by around 11 %). Changing the future PT-characteristics, compared to the basic scenario, results in decreasing emissions (8 to 10 %). The implementation of more trams in the future also results in decreasing emissions (about 10 %). The basic scenario, compared to all the variants applied, underestimates the future emissions in the case of less improvement of the emission parameters of the transport modes and in the case of higher growth of the future mobility demand. For all other variants the basic scenario results in about the same or higher future emissions than for the variants. Further improvement of the emission parameters results in the largest decrease of emissions, compared to the basic scenario. The introduction of Kolibri will result in an about 10 % reduction of future emissions of all air pollutants studied. The results will be almost nullified when the future mobility demand will increase more than expected, because of the introduction of Kolibri. The future emissions of cars will dominate the total emissions in all variants. The emissions of PT will substantially be reduced. The overall conclusion can be that improving PT in the future, and mainly the introduction of trams, can result in decreasing emissions of the local air pollutants studied.