کاهش انتشار PM, NOx و CO2 از طریق سیاستهای مدیریت سرعت در اروپا

Speed reduction measures rank among the most common schemes to improve traffic safety. Recently many urban streets or entire districts were converted into 30 kph zones and in many European countries the maximum permissible speed of trucks on motorways is under discussion. However, besides contributing to traffic safety, reducing the maximum speed is also seen as beneficial to the environment due to the associated reduced fuel consumption and lower emissions. These claims however are often unsubstantiated.To gain greater insight into the impact of speed management policies on emissions, this paper examines the impact on different traffic types (urban versus highway traffic) with different modelling approaches (microscopic versus macroscopic). Emissions were calculated for specific types of vehicles with the microscopic VeTESS-tool using real-world driving cycles and compared with the results obtained using generalized Copert-like macroscopic methodologies. We analyzed the relative change in pollutants emitted before and after the implementation of a speed reduction measure for passenger cars on local roads (50–30 kph) and trucks on motorways (90–80 kph). Results indicate that emissions of most classic pollutants for the research undertaken do not rise or fall dramatically. For the passenger cars both methods indicate only minor changes to the emissions of NOx and CO2. For PM, the macroscopic approach predicts a moderate increase in emissions whereas microscopic results indicate a significant decrease. The effects of specific speed reduction schemes on PM emissions from trucks are ambiguous but lower maximums speed for trucks consistently result in lower emissions of CO2 and lower fuel consumption. These results illustrate the scientific uncertainties that policy makers face when considering the implementation of speed management policies.

Road transport provides economic and social benefits for the entire society. Unfortunately, traffic also causes a number of unwanted effects like congestion, traffic accidents and traffic related air pollution. To counter these negative impacts, local policy makers in Europe have introduced, amongst other measures, permanent or temporary speed restrictions aimed at improving traffic flows, traffic safety or both. The conversion of entire districts, streets or street sections into 30 kph zones is usually done near schools or in residential areas where the previous speed limit was 50 kph. These measures, mainly aimed at increasing traffic safety and promoting cycling or walking, are usually seen or even promoted by local authorities as being also beneficial to the environment because of reduced emissions and lower exposure of inhabitants or other road users (Joumard, 1987, Anderson et al., 1997 and Int Panis et al., 2010). The claims for these environmental benefits stem from the belief that speed reduction measures in urban areas have similar benefits as those on motorways (Keller et al., 2008 and Keuken et al., 2010). However, in contrast to this popular belief, wide spread emission estimation methods using quadratic functions, such as the European Copert/MEET approach (Ntziachristos, 2009) predict that emissions may even rise dramatically and for this reason urban speed reduction policies are sometimes vigorously opposed. Copert (Computer Program to calculate emissions from road traffic) is based on average speed emission factors to estimate emissions on a macroscopic level (e.g. the national level; see examples in Beckx et al., 2009). Unfortunately, the speeds typical for urban traffic (especially congested traffic) are very close to or lower than what is usually considered to be the minimum average trip speed for which relevant estimates can still be made using this macroscopic approach. Therefore, more sophisticated methods are needed to estimate the impact of the introduction of low speed zones on vehicle exhaust emissions in urban areas. Using microscopic models permits for the accounting of lower average speeds which may also be associated with less variability resulting in environmental benefits (Int Panis et al., 2006 and Beusen et al., 2009). Similarly, the reduction of the maximum speed of trucks is under discussion in several European countries. Reducing the speed limit for trucks from 90 to 80 kph is seen as beneficial for traffic safety and for the environment (Dijkema et al., 2008). However, this implementation often results in criticism from (economic) stakeholders and policy makers in relation to time and economic losses, in addition to casting doubts over the assumed environmental and safety benefits. Unfortunately, scientific analysis is often unavailable or ignored in the political discussions on this theme. In this paper, we shed some light on the environmental impacts of speed management policies by presenting the results from two different approaches: a sophisticated vehicle based microscopic emission modelling approach based on detailed second-by-second driving cycles (using the VeTESS model) and the traditional macroscopic approach based on average speeds (using a Copert-type model). The impact of speed measures on vehicle emissions is evaluated with both modelling approaches in two different settings (urban versus highway). Both types of models have some drawbacks but by combining results of two complementary models we can gain a better and more robust understanding of the potential impact of different speed management policies on exhaust emissions.

The results of this paper demonstrate that it is unlikely that strict speed limits in urban environments will have a significant influence on the emissions of NOx or CO2. Regarding the impact on emissions of PM the microscopic results indicate that the exhaust from the diesel vehicles may show a significant decrease, whereas the macroscopic approach assumes a moderate increase. Considering these results, policy makers should cautiously interpret emission modelling results that estimate the impact of speed reduction policies on emissions in urban areas. Changing speed limits in urban environments should mainly be considered from a safety perspective. The impact on the environment should not be the deciding factor to tip the balance between implementing and not implementing lower speed limits. Further, lower interurban speed limits are often portrayed as being good for the environment but bad for the economy. Our analysis of changing speed limits for trucks from 90 to 80 kph generally confirmed the environmental benefit. All results for trucks consistently indicate that lower maximum speeds for trucks on motorways result in lower emissions of CO2. Results for NOx and PM are not consistent. The impact on the economy and traffic safety was not discussed. The results presented in this paper demonstrate that estimating the impact of speed limit reductions on emissions from vehicles is a complex endeavour. Estimating the impact of policies on emissions and air quality is even more difficult (Int Panis et al., 2006 and Beckx et al., 2009), an inconvenience that is often overlooked but crucial in deciding on environmental transport policies. More and more environmental policy makers nowadays rely on computer models to test traffic policies. The results in this paper illustrate the scientific uncertainties that policy makers face when considering the implementation of speed management policies and demonstrate that evaluations of speed management policies should not exclusively rely on a macroscopic assessment.