Measuring the acoustic properties of audio tactile road markings

Audio tactile or "structured" road markings are a good choice as edge line on high speed roads, on the first place for ensuring night time visibility (retroreflection) during rain. However, vehicles accidentally crossing it produce extra tyre/road noise and the sound increase inside the car can be considered as a positive side effect, as it alarms the driver and may be very helpful for the prevention of "doze off" traffic accidents. The external noise on the other hand may have a positive aspect as well as it can warn people on the emergency lane about the approaching vehicle, but it may also annoy people living around. The growing popularity of structured road markings makes it desirable that there exists a standardized measurement method to assess the noise production of such markings. It should be representative, reproducible, generally applicable and as simple as possible. A method to assess the "exterior noise", mainly based on the "Close Proximity" method, an ISO method intended for the acoustic assessment of pavements, has been proposed a few years ago as a contribution to the work of the CEN working group "road markings" (CEN/TC226/WG2). This paper reports the results of two round robin tests which have been carried out in 2015 and 2016, each with three participants with their own CPX trailer. Both tests have been done on a special test site with eight audio tactile road markings and were intended to assess the feasibility of the method and the reproducibility of the results.