Modeling the Probability of a Collision Given the Lateral Offset and Size of a Narrow-Fixed Object

Determining the conditional probability of a crash with a narrow-fixed object (NFO) given an encroachment has occurred, P(C|ENCR) has been computationally burdensome leading to the development and reliance on software by roadside safety engineers. The objective of this study was to develop a simple model to represent P(C|ENCR) when the size of and the offset to an NFO are known. This paper presents a model developed from the field collected data available within the third version of the roadside safety analysis program (RSAPv3) to represent P(C|ENCR) for individual NFOs. This model is an equation which can be applied to NFOs across a variety of diameters and offsets from the travel way. The use of this model will allow for quick computations to determine the probability of a crash with an NFO across a variety of offsets and diameters without the necessity to run software. Models are presented for both heavy vehicles and passenger vehicles. The methodology, datasets, and analysis used are documented. This research led to an improved understanding of the influence of offset and diameter on the probability of a crash. Models such as these reduce the dependence on computationally intense software programs and allow the analysis of safety to be more transparent.