Integration of Pavement Roughness into Safety Performance Functions of Two-Lane Rural Roads in Pennsylvania

Existing approaches to infrastructure management neglect the impact of infrastructure condition on safety performance, even though poorly maintained roadways can contribute to increased crash frequencies. This is perhaps because very few studies have quantified the impact of infrastructure condition on safety performance. Hence, this work develops safety performance function (SPF) models that relate pavement condition - specifically, roughness, as measured using the international roughness index (IRI) - and other roadway factors with observed crash frequencies. These SPFs are then combined with pavement roughness deterioration models to better understand how maintenance decisions can be used to improve roadway safety performance. Data from two-lane rural roadways in Pennsylvania are used for this effort. The SPF estimation results reveal that accounting for IRI in SPF development significantly improves model fit, and that IRI has a significant and positive impact on crash outcomes. The results further suggest that the IRI has a different impact on total crash frequency as compared to fatal and injury crash frequency, and rear-end crashes. This is likely due to how roughness of the roadway can impact travel speeds. Finally, the results also show that maintenance activities that reduce IRI can have significant safety benefits. This suggests that pavement management decisions should also consider the anticipated safety benefits, in addition to other factors.