The primary objective of this study was to provide guidelines and tools for quantifying the environmental impacts in terms of fuel consumption and emissions of various highway geometric design conditions related to crest vertical curves. Second-by-second speed profiles were generated with speed prediction and polynomial models, and fuel consumption and emission rates based on vehicle-specific power and speed were extracted with the recently developed motor vehicle emission simulator (MOVES) modeling software. The generated speed profiles were matched with the extracted rates and aggregated during a trip on the curves. A benefit–cost analysis was also carried out with existing data from Washington State. The results demonstrated that the design vehicle respectively consumed and produced 10% less fuel and carbon dioxide on the crest vertical curve designed with a rate 1.5 times greater than the minimum rate of the vertical curvature documented in the AASHTO Green Book. For other emissions—carbon monoxide, oxides of nitrogen, hydrocarbons, and particulate matter of 2.5 μm or less—there were also reductions by up to 31% on the curve. The results also showed that the environmental economic benefits from flattening the curve design exceeded additional construction costs for a 30-year design period. Vertical curve design providing a flattened curvature can be environmentally and economically beneficial throughout the life of the highway. This study shows the efficacy of environmentally friendly design for sustainable transportation.