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Publication Number: FHWA-HRT-07-059
Date: October 2007
Updates to Research on Recommended Minimum Levels for Pavement Marking Retroreflectivity to Meet Driver Night Visibility Needs
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8. FUTURE RESEARCH NEEDS
The results of this study indicate that it would be beneficial to conduct additional research before implementing minimum pavement marking retroreflectivity values. This research effort did not include the collection of any field data to support the findings. Therefore, the recommendations should be validated by field testing to determine if the recommended minimum retroreflectivity levels provide adequate information to drivers under various speeds, roadway geometries, lighting conditions, and vehicle geometries.
This study determined minimum pavement marking retroreflectivity for straight roadways. The need exists for research showing how these values are affected by horizontal and vertical curves. Under such geometric conditions, the pavement markings will be located in different areas of a projected headlamp beam, having a significant impact upon their visibility.
Most of the pavement marking nonsubjective visibility research has been conducted with research participants viewing markings in a static condition or while driving at relatively slow speeds ( 48.3 km/h (30 mi/h ), for example). There is little research showing what drivers need in terms of preview time and pavement marking luminance under high-speed conditions. Such research could help determine if assuming one required preview time for all speeds is necessary. As such, methodology tends to produce relatively high minimum retroreflectivity values for high speeds using preview times in the middle of the typical range used. Additional research into preview time required by drivers would also be beneficial, as previous recommendations of minimum pavement marking retroreflectivity have used a wide range of preview times, resulting in a wide range of recommended values. Utilizing a reasonable preview time is critical in determining minimum pavement marking retroreflectivity.
While some research shows that increasing line width can increase detection distance, other research on this issue has been inconclusive. Further research is needed to determine if widening pavement marking lines does, in fact, enhance visibility and if that enhancement translates to lower required pavement marking retroreflectivity. The Texas DOT is planning to commission a study starting in September 2007 that provides an opportunity to direct further research on the effectiveness of line width.
Research findings do show that roadway lighting increases the visibility of pavement markings. However, this research is qualitative and subjective in nature. A need exists to quantify the interaction between pavement marking visibility and the presence of roadway lighting as well as to understand the optimum roadway lighting deployment strategy that maximizes pavement- marking visibility.
Research findings from TTI and 3M show that there are differences in the performance of marking materials as a function of geometry.(44) Markings with similar 30-m (98-ft) RL values can have very different visibility distances because of very different luminance levels beyond the standard 30-m (98-ft) measurement geometry. Therefore, a need exists to better characterize different types of pavement markings to better understand how different marking materials behave when the geometry is varied.
Finally, there have been a few research efforts th at provide insight into the interaction between pavement markings and RRPMs. While the quantitative simulator research and the qualitative field research completed to date have increased understanding in this area, further research is necessary to understand driver information needs from pavement markings when RRPMs are used. Also, better information regarding the degradation of RRPM visibility would aid in developing more refined discount factors for pavement marking retroreflectivity.