Longitudinal evenness is an important influencing factor as well on road safety (ruts, aquaplaning) and ride comfort as on the durability of roads (increased dynamic axle loads of trucks). The wavelengths covered by longitudinal evenness range from 0.5 to 50 m. Different approaches have been made over the years to describe and judge the different forms of (un-)evenness, mainly periodic and irregular discontinuities and singular events. Each of these descriptive parameters has another weakness, most of them not covering periodic discontinuities. In Austria, the International Roughness Index (IRI) is in use for pavement management systems at present, the 4 m-straight edge is used for acceptance tests. Both methods have their own problems: The IRI is not capable to detect periodic discontinuities and is – overall – a rather inaccurate parameter, while the 4 m-straight edge is unable to cover longer wavelengths. To overcome these shortcomings, a research project was started to develop a better parameter as well for pavement management as for acceptance tests. After a comprehensive literature review thirty test sections containing all different aspects of longitudinal evenness problems were picked out. The focus was set on a good representation of the different road designs used in Austria (asphalt, asphalt concrete, concrete), different age of the pavements and different types of roads (motorways, city streets, …) These sections were measured with a high speed laser profilometer (RoadSTAR) and true profiles where calculated. Then, the true profiles were examined and a characterization of the profiles was done. Knowing the “real” unevenness of the sections, different parameters (PSD, IRI, AUN, LWI, …) from the literature review were applied on the profiles to see how good these parameters judge the evenness problems. The weighted longitudinal profile showed good results and is able to judge all relevant phenomena of longitudinal evenness. The used weighting function allows the user to adjust for his own highway level characteristics. A detailed investigation with this parameter on network level has still to be done. (Author/publisher)
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