Transport add-on environmental modelling system (TRAEMS) is a GIS-based environmental modelling system designed to evaluate the environmental consequences of road traffic in urban areas. Its development has been underpinned by the premises that the evaluation of road traffic impacts is best undertaken during the early planning stages of road networks, and that this can utilise much of the data generated by the transport planners themselves as they apply their travel demand models as to planning of road networks. The system integrates information about traffic-usually from travel-forecasting models-with information about land use, to provide the input data to a range of commonly used models that estimate pollution from a road traffic system, and the energy consumption of that system. TRAEMS facilitates this integration and allows land use, transport and environmental planners to have rapid feedback on the environmental effects of road transport network scenarios that are being developed and tested. Its purpose is to aid in the selection of environmentally-preferred road networks and to highlight where management of pollution levels on future road networks will be required. TRAEMS has a modular structure. This paper describes the main features of the air pollution and fuel consumption modules of the system and illustrates the system's utility through case studies at both metropolitan-wide- and local-area scales.