This study used fuel consumption and emissions on horizontal curves to provide guidelines and tools for quantifying environmental impacts. The second-by-second speed profiles for various conditions were generated on the basis of speed prediction and polynomial models. The generated speed profiles were matched with the rates of fuel consumption and emissions from the most recently developed motor vehicle emission simulator. Then, fuel consumption and emissions per second were aggregated during a trip on the curves. The results demonstrated that the design vehicle with a speed of 70 km/h consumed 34% more fuel on the curve that was designed with a 50% reduced radius than the recommended minimum standard in the Green Book. For emissions—carbon monoxide, nitrogen oxides, hydrocarbons, and particulate matter of 2.5 microns or less—there were increases up to 91% on the curve. In the benefit–cost analysis with actual horizontal curves with a radius less than half the minimum standard, the curve design improvement with the recommended minimum standard contributed to reducing fuel consumption, emissions, travel time, and societal and health effects, as well as construction and operating costs, by shorter length of alignment. Thus, horizontal curve design with the recommended minimum standards can be environmentally and economically beneficial throughout the life of the highway. This research also shows that adverse environmental impacts from vehicle movements on highways can be controlled and reduced through environmentally conscious highway design.