This paper introduces the results of a research project on the pollutant emissions and fuel consumption characteristics of mixed traffic streams under different levels of congestion. The project involved extensive testing of a number of vehicles, both on-road and in the laboratory, to determine their fuel consumption and emissions characteristics under different traffic conditions. A set of models for different vehicle types were then assembled, based on the hierarchical family of models for fuel consumption presented by Biggs and Akcelik (1986), which was also capable of describing vehicle emission rates. The model family consists of models at four levels, from an 'instantaneous' model for individual vehicles driven in traffic, through an 'elemental' model suitable for studies of intersection behaviour, a 'link' model suitable for transport network analysis, and a 'journey' model suitable for land use planning applications. The models for individual vehicle types may be combined to yield models for the performance of a traffic stream. These models may then be incorporated into transport network analysis performance, as tools for use in the prediction of environmental and energy impacts of road transport projects. One such integration of the models into a super-model (IMPAECT) for environmental impact analysis of transport planning decisions is described. The focus is on the development and application of the energy and emissions models, which are made up of three sub-models: (1) traffic stream composition sub-models, to determine the emissions or fuel consumption of a traffic stream as an aggregate of the vehicles in that stream, (2) congestion functions, to relate travel conditions (delays, queuing and speed-time trajectories) to traffic flows on particular types of roads, and (3) sub-models of vehicle energy and emissions performance under different traffic conditions. (A) For the covering abstract see IRRD 886400.

This paper considers the development of a method to assess the impacts of transport systems on the urban environment and for investigating plans to ameliorate adverse environmental impacts in a region. The method draws on models for transport network analysis and for fuel consumption and emissions modeling. Models permitting: (1) the examination of alternative policies and broad strategies for metropolitan travel, and (2) alternative vehicle and fuel technologies, are included in the system. The paper indicates how these procedures are being integrated into an environmental impact assessment package, or supermodel, known as IMPAECT (Impact Model for Prediction and Assessment of the Environmental Consequences of Traffic). IMPAECT consists of a set of four PC-based computer models linked through a common data structure. The component models are a traffic network model, a vehicle energy and emissions (air and noise) model, a pollutant dispersion model and a land use impact model. The modular design of the supermodel allows the use of alternative components, to suit local needs and thus enhance flexibility of use.

This paper outlines some of the interactions and relationships between traffic/transport systems, land-use and environmental amenity, leading to a detailed discussion of a PC-based environmental impact assessment system.The system consists of a traffic network model, a vehicle energy and emissions (noise and air) model, a pollutant dispersion model and a land-use impact model. The vehicle energy and emissions model estimates the energy used; and the levels of noise and air pollution generated from traffic streams. These traffic streams are a function of traffic flow, travel conditions, vehicle type and fuel type. The assessment system will allow the user to predict and assess the environmental impact of road traffic, transport infrastructure and travel demand management schemes. The system has the ability to detect relative differences in levels of pollution and energyuse between alternative schemes, while the schemes are still in the planning stage. Considerable community benefits will result from the use of a method whereby route and facility location decisions can be made with fullknowledge of the possible impacts. (a) For the covering entry of this conference, see IRRD abstract no 861490.