The Refinement of Drivers’ Visibility Needs During Wet Night Conditions: Wet Visibility Project Phase III

About the report:

The purpose of this project was to develop a specification for the minimum retroreflectivity of pavement markings in wet nighttime conditions.  In order to establish this specification, the performance of four retroreflective pavement marking materials in wet-night conditions was evaluated.  The performance of the pavement markings was evaluated by driver participants under simulated rain conditions using a similar protocol to studies that have already been performed at the Virginia Tech Transportation Institute.  The performance of the markings was verified based on the participants’ ability to detect the end points of the markings in both rainy and clear conditions. 

The conclusions from this investigation indicate the following:

• The materials developed over recent years show an improved performance over those tested previously.  These materials provide adequate performance through improved technology and performance.
• The log-linear relationship found previously is functional for the data provided. Two models were developed.  The model with no intercept provides a more constrictive boundary at low levels of retroreflectivity.
• A retroreflectivity value above 250 mcd/m2/lx provides limited return in terms of detection distance.
• A specification limit of 150 mcd/m2/lx will provide adequate visibility for 55 mph in dry conditions and 40 mph in wet conditions using standard dry retroreflectivity measurements, and 1 in/hr measurements for the wet conditions.  This value should be the minimum maintained over the life of the marking.
• The retroreflectivity specification for a white and a yellow material should be equal.
• The rumble stripe showed a significant recovery time improvement over the other tested materials.

This study recommends a minimum retroreflectivity of 150 mcd/m2/lx for white and yellow pavement markings in both dry and wet nighttime conditions.  This level provides the Virginia Department of Transportation with the basis for establishing a performance-based specification for pavement markings.

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