Effects of Pavement Surface Roughness and Congestion on Expected Freeway Traffic Energy Consumption

In life-cycle assessments of roadway infrastructure projects, the significant amount of energy consumed during the use phase has been largely ignored when decisions related to roadway construction and rehabilitation have been evaluated. Traffic congestion, pavement types, and surface roughness conditions affect energy consumption throughout the use phase. This study developed an integrated modeling framework that accounted for the effects of pavement roughness degradation on estimated energy consumption for freeways and other restricted access highways, considering vehicle types and traffic growth, as well as congestion patterns. The framework was achieved through three interdependent modules: Module 1 estimated vehicle specific power (VSP) by relating the International Roughness Index (IRI) of pavements to coefficients used in the Environmental Protection Agency’s motor vehicle emission simulator, Module 2 used the state-of-the-art cell transmission model to predict traffic evolution and congestion on the freeway and determined the total vehicle miles traveled at a spectrum of speed ranges, and Module 3 estimated energy consumption from an IRI profile, VSP coefficients, and traffic speed–miles profile. A case study confirmed that IRI and congestion had significant impacts on estimates of energy consumption during the use phase. The study showed that ignoring IRI variation or traffic congestion could lead to underestimations in VSP by up to 2.5% and energy consumption by approximately 6%.