During the last ten years, dry road marking retro reflectivity has been measured by the use of mobile equipment. However, due to a growing interest in the performance of wet road markings, the use of road markings with a profiled surface is common in many European countries today. When measuring this type of marking with the use of mobile equipment in wet weather conditions, one problem arises: The measured retroreflectivity will be affected by splash from the wheels of the measurement vehicle, which can be avoided only by driving extremely slowly. Therefore, in order to carry out measurement at the speed of surrounding traffic, measurements must be accomplished on dry road markings.
So far, regarding mobile measurement, wet road marking retroreflectivity has been predicted using a model involving the dry road marking retroreflectivity and the mean profile depth, MPD, of the profile. However, the precision of the predictions is poor and there is a desire to improve the model. One hypothesis is that another measure than MPD would have a higher predictive value. This measure should take into account the area of all facets that are oriented in directions towards the driver.
In a first step of the study the so-called texture factor, T, was developed. In short, this texture factor calculates the sum of the luminous flux from all road marking facets which are visible to the driver. In the next step, using results from field measurements, a prediction model was developed and evaluated.
The result shows that the fundamental hypothesis can be accepted: The texture factor is a better predictor of the retroreflectivity of a wet road marking than MPD is. The conclusion of this study is that an important step towards a better prediction model for wet road marking retroreflectivity was taken. However, collection of more data and the introduction of an indicator for contribution from glass beads would probably improve the model even more.