The purpose of this paper was to further investigate a previously developed basic consistency model that was applicable mainly to level terrain and to enhance it to include the impact of grades and trucks on consistency; to present an original, independent software program that determines the speed profiles of cars and trucks based on both horizontal and vertical alignment features; and to present the investigation and results of the impact of design consistency on road crashes. An enhanced consistency model that includes an exponential term to quantify the impact of trucks on consistency is presented and evaluated. The software and its logic and algorithms are presented along with a sample analysis of two short highway segments. A statistically significant trend showing a reduction in crash rates with an increase in consistency is discussed. The model and the software may be used to determine consistencies of different alternatives during the planning of new highways or the reconstruction of existing roads, alerting users to potential design deficiencies, thus improving safety levels and helping to save lives. (a).
Abstract