ON HIGHWAY FUEL AND TIME EXPENDITURES

This paper investigates the influence of slopes along the highway, which are determined as part of the vertical alignment, on the main parts of the user cost, namely, fuel cost and travel time value. If each time unit is evaluated at not less than a value derived for it by a revealed preference method (from the driver's speed choice), then the sum of the fuel and time costs is a convex function of the slope. This sum is a convex function of the (traffic) flow. However, if the fuel cost alone is taken, no convex function for either of these cases is obtained. The convexity of the fuel and time costs are used to show that the vertical alignment problem is convex too.