Categorical modeling to evaluate road safety at the planning level

Abstract

The most efficient strategy to ensure long term road network safety is to integrate road safety analysis into the planning process of a network or a corridor. Safety planning decision-support tool outcomes should be reliable and realistic, taking into account the main characteristics of this particular level, which is characterized by scant and generalized data. However, the tools developed and presented in previous studies are based on models with a quantitative response, usually the number of accidents, which may not be appropriate for this level. In order to develop a more suitable tool while maintaining a measure assessment character, this work presents a qualitative response model whose outcome is the risk of occurring three degrees of hazards: low, medium and high. In the present study, an ordered probit model was applied to an urban road network using Porto (Portugal) data covering a 5-year period. Hazard categories were defined using accident frequency to reflect a measure of the safety of the road network studied. The developed model provides a safety risk analysis of a road network or a corridor for a future period, considering road data that are easy to gather or estimate at the planning level, such as land use, traffic volume, etc. This methodology was applied to various segment scenarios to provide an evaluation of changing road features. Furthermore, a comparison between qualitative and quantitative model outcomes is presented, showing the former as an appropriate model that enables a risk analysis approach.