The Road and Hydraulic Engineering Division of the Dutch Ministry of Transport, Public Works and Water Management is investigating the possibilities of creating road markings on motorways that warn drivers against leaving the main carriageway. In order to minimize the additional noise pollution for the locality, the aim of this project is to find an alternative for the existing rib edge lining which is based on creating an acoustic warning signal. The TNO Institute of Applied Physics (TPD) has contributed to the design of a raised pattern that causes perceptible vibration in vehicles driving over the pattern without an acoustic signal. In the Netherlands the first experiments with the raised pattern were carried out on a stretch of test road on the A50 motorway. The raised pattern, with a shape that differs slightly from the proposed one, created virtually no extra noise, but its warning function fell short of expectations. The results of the first experiments led to a modification of the shape of the raised pattern and new measurements were carried out by the TPD on a stretch of test road on the A28 motorway. Although for passenger vehicles an increase of the sound pressure level of 2,5 dB(A) to 4,5 dB(A) was measured at the moment their wheels touch the line, the increase of the equivalent noise level (LAeq) is not significant when the average duration of such increases is taken into account. When touching the road marking the vibration level in passenger vehicles increases strongly in certain 1/3 octave bands, corresponding to the distance between the ripples of the pattern and the velocity of the vehicle. This results in a clear warning to the driver. However, the vibration levels seem to decrease as the weight of the vehicle increases. For the heaviest truck that was used for the experiments, the warning function is not quite satisfactory.
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