Safety and Highway Investment

This monograph examines issues related to the valuation of accident cost saving and the estimation of accident rate reductions likely to be associated with highway investments. The two primary purposes of this research were to 1) develop a practical method for estimating the reduction in accident risk if a roadway is improved and 2) shed light on the appropriate value to be assigned to a reduction in accidents. Chapter 1 contains an overview of the study. Chapter 2 considers in detail the question of how to valuate the safety benefits of highway investments. Information on how state departments of transportation (DOTs) currently evaluate safety benefits was obtained by a survey, the results of which are described in Chapter 3. These results show that state DOTs vary in the values they assign to decreases in accident risks. Most still use a value that is less than the value that the Federal Highway Administration (FHWA) requires to be used in evaluating safety benefits of federally funded projects. The other piece of information needed to estimate the safety benefits of a project--how the project affects the rate and type of accidents--can be obtained from data on accidents and road characteristics. Detailed data bases developed by the Iowa DOT are used to analyze the relationships between road characteristics, accident rates, and accident costs; the results are presented in Chapter 4. The predictive models that were developed enable accident rates and costs of an illustrative two-lane road to be compared with those likely if a specific upgrade were made. Also tested are the sensitivity of accident cost saving per million vehicle miles of travel to the dollar values assigned to reductions in fatal, personal injury, and property damage accidents. Chapter 5 summarizes the research findings and offers three recommendations to improve the ability of state DOTs to take accident cost saving into account when evaluating potential highway investments.