Description

This initial proposal document sets out the rationale, objectives, and preliminary technical approach for incorporating environmental exhaust emission modeling into HDM-4 under the ISOHDM research framework. Recognizing that traditional road appraisal tools focused almost exclusively on economic costs to road agencies and vehicle operators, this paper argues for the inclusion of environmental externalities to support sustainable transport planning. The document outlines the target pollutants—including greenhouse gases like CO2 and local air contaminants such as CO, HC, NOx, and lead—and reviews candidate emission modeling approaches ranging from simple speed-based functions to detailed power-demand models. Key input requirements are identified, such as traffic volumes, fleet composition, vehicle technology types, road geometry (vertical grades), and fuel properties. The proposal defines a work plan for developing computationally efficient algorithms suitable for network-level planning without requiring overly complex microscopic traffic data. This baseline document laid the ground work for subsequent ISOHDM technical working groups to establish formal exhaust emission relationships within the HDM-4 system. Overall, the report emphasizes rigorous empirical validation, standardized data acquisition protocols, and modular integration into the broader Highway Development and Management analytical engine. By combining physical principles with statistical calibration across international trial sites, this working paper provides a robust theoretical and practical baseline for highway authorities to evaluate long-term infrastructure policy options, allocate maintenance budgets efficiently, and maximize economic returns across regional and national road networks. In summary, this study provides highway engineers, transport planners, and economic analysts with an essential mechanistic-empirical tool for evaluating life-cycle infrastructure costs, optimizing maintenance