An analysis of the safety effectiveness of pavement marking retroreflectivity
It has been shown in previous research that greater longitudinal pavement marking retroreflectivity levels increase drivers' visibility and detection distance. However, increased visibility may also cause drivers to feel too comfortable during nighttime conditions and drivers may then pay less attention and/or operate at unsafe speeds. Before-and-after studies have been conducted on pavement marking improvements such as repainting stripes or changing to a more durable marking material. Studies have also used models to estimate the retroreflectivity based on the date of installment, the vehicle exposure, or assumed a linear reduction in retroreflectivity over time. Only two studies have related measured pavement marking retroreflectivity to safety performance (crash) data. This study analyzes the relationship between 3 years of pavement marking retroreflectivity data collected by the Iowa DOT on all state primary roads and corresponding crash and traffic data. This study developed a spatial-temporal database using measured retroreflectivity data to account for the deterioration of pavement markings over time along with a statewide crash data to attempt to quantify a relationship. Three different sets of data were analyzed: the complete database, two-lane roads, and records with low retroreflectivity values (≤ 200 mcd/m2/lx) only. The distributions and models of the entire database and the two-lane records did not show that poor pavement marking retroreflectivity correlating to a higher crash probability. When looking at records with low retroreflectivity values only, a statistically significant relationship was determined. However, the correlation was so small it does not have practical significance.