A central theme of this book is the necessity to take proper account of the full impacts of traffic system developments. This will certainly include consideration of environmental impacts. The performance of traffic systems can have strong environmental impacts, certainly at the local level and most likely at the global level, when individual contributions are aggregated to consider issues such as greenhouse gas emissions. Road traffic systems have significant impacts on fuel consumption by vehicles and environmental degradation in regions. Particular concerns in traffic analysis have arisen with respect to: • fuel consumption and means of conserving fossil fuels; • air pollution, including gases and particulates; • noise and vibration, and • visual intrusion and physical degradation.