Modeling In-Use Construction Equipment Emissions for Highway Projects

Interest in estimating the air pollutant emissions that occur during highway project construction is increasing. This paper describes a construction emissions modeling framework with companion calculation methodologies. On the basis of bid data and field data collected from a range of highway construction projects, the modeling framework builds linkages between material quantities, equipment in-use hours, and pollutant emissions. The data calculation and processing methodologies can assist project analysts in creating emissions estimates across various construction operations at early environmental assessment stages when, typically, limited data are available for characterizing equipment activity for the future project. A hypothetical freeway-widening case study was used to demonstrate the application of the modeling framework and calculation methodologies. The example illustrates the framework's ability to disaggregate emissions by construction operation; in the case analysis, hours of equipment use and emissions were greatest during roadway excavation and foundation work. Project analysts can also vary individual equipment characteristics that affect emissions, such as tier group (emissions certification standards), horsepower rating, equipment deterioration, and other factors in construction emissions analyses. For example, the emissions reduction benefits of shifting the equipment fleet to more stringent (Tier 4) emissions standards, especially as a strategy for reducing particulate emissions, can be quantified.