Optimizing Road Gradients Regarding Earthwork Cost, Fuel Cost, and Tank-to-Wheel Emissions

Abstract

Emissions reduction has emerged as one of the principal targets in the planning and designing of road alignment today, and intelligent design methods can help optimize road alignment as a response toward more sustainable road infrastructures. The largest share of emissions in road transport occurs in the use phase; hence, considering vehicles’ behavior already in the early stages of the planning process is crucial. This study compares earthwork costs, fuel costs, and tank-to-wheel emissions of alternative road vertical alignments using a spline linear programming (LP) optimization method. The traditional minimal earthwork cost model is tailored and augmented with a fuel item to account for vehicle fuel costs. Three options are considered, including an earthwork-based (EW) optimal road alignment, a balanced earthwork-and-fuel cost (EW-FC) optimal alignment, and a minimal fuel cost (FC) alignment. Calculations are done for a reference test heavy-duty vehicle assumed to operate at uniform speed. The results exhibited that, although leading to some increase in earthwork costs, a design for balanced EW-FC cost yields substantial fuel budget and related emissions savings.