Evaluation of the impact of pavement roughness on carbon dioxide originating from vehicles

Several gases originating from the land transportation mode are considered as greenhouse gases (GHG) and therefore are among elements that contribute to global warming. Both the amount and the type of gas emitted depend on factors such as vehicle type, engine size, ambient temperature, congestion, traffic flow, vehicle age, fuel type, frequent deceleration and acceleration, travelled distance and vehicle speed. Among all the types of GHG, carbon dioxide (CO 2) will be the main focus in this study as it is the most widespread GHG produced by automobiles according to the Environmental Protection Agency. On the other hand, the pavement condition, in terms of its roughness, could be one factor affecting vehicle speeds. With pavement roughness affecting vehicle speeds and speed affecting GHG emissions, one may suggest that the roadway pavement roughness may indirectly affect CO2 emission rates. The objective of this study is to investigate the correlation between CO 2 emissions and the pavement roughness. The pavement roughness measurement used in this study is the International Roughness Index (IRI). IRI data were obtained from the Maryland State Highway Administration. Speed data were collected on selected roads in Baltimore County (Maryland). CO2 emissions quantities were computed using MOVES2010a, a vehicle emission modeling software program. There are two steps involved in determining the relationship between IRI and CO2 emissions: (1) verifying that IRI numbers have an impact on vehicle speeds and (2) verifying that vehicle speeds have an impact on CO2 emissions. The results from the analysis indicate a slight increase in the mean speed value from roads in poor condition to roads in either fair or good condition and therefore a decrease in CO2 emissions. The findings of this research could help agencies to properly allocate roadway maintenance funds in the intention of reducing the environmental impacts associated with pavement roughness.