At rural highway speeds, road roughness is a source of undesirable dynamic forces and displacement in the interaction between road, vehicle and human. These vibrations can cause a sense of discomfort, and it cannot be ruled out that they could impair the health and performance ability of both drivers and passengers alike. A study has therefore been conducted on National Highway 90 and County Road 950, aimed at ascertaining the seriousness of the problem of whole-body vibration during travel. The roughness index on the test stretches varied from very good (IRI20 = 0.43 mm/m) to extremely poor (IRI20 = 22.78 mm/m). Vibrations that affect vehicle occupants were measured in different configurations of moving timber lorries and ambulances. A separate report published by Ingemansson Technology AB presents a detailed account of how the measurements were carried out and how the data was stored and analysed. Another separate report published by the National Institute for Working Life presents the findings from an analysis of the effect on the human body of the vibrations recorded. This report is a summary of the study. It also contains an interpretation of the findings from collating the vibration measurement data with the data collected in connection with the routine annual road condition surveys. There are three main causes of vibration: road roughness, vehicle properties and driver behaviour (including the choice of speed). The results of this study support the opinion that, within reasonable variations in these factors, road roughness has a far greater impact than the other two variables. Further, the study substantiates that the higher frequency of injury, especially in commercial drivers’ locomotor systems (as been found in earlier studies), is related to rough roads. This correlation is probably strongest in geographical areas where long stretches on a large percentage of the roads have a high IRI, i.e. in the so-called ”forest counties” of Norrland, Värmland and Dalarna in Sweden. Riding the roughest road stretches, peak values were registered on the ambulance stretchers with vibration levels that are considerably above levels that completely healthy people are considered to experience as ”extremely uncomfortable”, as per an international standard on evaluation of human exposure to wholebody vibration. (Author/publisher)
Abstract