dEVElOpMEnT OF an inFRaSTRucTuRE cOEFFiciEnT BY an analYTic hiERaRchY pROcESS and iTS RElaTiOnShip TO SaFETY

The study has four main objectives: (1) to test the correlation between different infrastructure characteristics and crash-rates, and trends; (2) to develop an Infrastructure Coefficient (IC) that represents the overall infrastructure characteristics of two-lane rural highways; (3) to develop a crash-prediction model for two-lane rural highways in which the IC developed is the independent variable; and (4) to estimate and quantify the contribution of the infrastructure as a whole to highway crashes. Infrastructure is defined in this study as the highway and its geometric features: alignment, road-side elements, sight-distances, presence of guardrails, access-points, roadway consistency, and additional variables that all together measure the overall infrastructure quality of a highway. The first phase in the development of the IC involves an examination of the correlation between different infrastructure characteristics and crash-rates. In the second phase, the Analytic Hierarchy Process (AHP) is utilized to develop the IC. Finally, a crash-rate prediction model that relates crash-rates to IC for two-lane rural highways is developed. The IC that was developed consists of a linear combination of five infrastructure characteristics: road consistency, lane width, road-side score, percentage of highway with a no-passing zone, and number of access points per unit length. These five characteristics were found to have the most significant contribution to safety among all the characteristics included in this study. A model for the prediction of crash rates based on the proposed IC is calibrated and presented. It is suggested that this model be used to evaluate the safety level of existing or planned highways. This study also found that, at a 99% confidence level, a highway with good infrastructure quality reduces crash-rates by 44% on average compared with a highway with poor infrastructure quality.