The velocity model in the existing VSS standards is based on physical calculations. The speeds are also actually driven as benchmarks. The speeds are influenced mainly by the road geometry and the speed limits. With regard to road geometry interesting addition to the relationship between turn radius and speed, the influence of the pitch on the speed behaviour. The influence of the pitch has been studied in the past in two research papers. In this time was on roads outside cities, the general speed limit 100 km / h. Since the introduction of general speed limit 80 km / h no investigations have been carried out in hills and slopes in Switzerland.
One of the main objectives of standardization is to allow new findings are incorporated continuously in the body of standards. Such findings relate to the changes in the relationship between pitch and speed of vehicles. Based on studies of the traffic flow are therefore on roads outside cities, the relationship between the size of the pitch and the speed behaviour of cars and trucks determined and the changes compared to the previous surveys are found. Because of this the Basics gene can be assessed whether a revision of the existing standards imposes. The focus is the VSS, standards SN are 640, 110, elements of vertical lines "and SN 640 138a, additional strips in gradients".
Based on studies of the traffic flow on roads to long distance relationships between the size of the pitch and the speed behaviour of cars and trucks determined and the changes compared to the previous surveys are found. Based on these results it can be assessed whether a revision of the existing standards imposes. The project will form the basis for standardization.
In order to implement in practice the existing VSS standard SN 640 138 revised. The work also makes an important contribution to the discussion of the impact of changes in the weight limit for heavy motor vehicles on the road infrastructure.
Here are crucial results of the project:
In the case of passenger cars (PCs), increased homogeneity was evident in the speed distribution of 1999 compared to earlier surveys of 1978. The speed difference between the fast (V85%) and slow (V15%) PCs is about 20 km/h, irrespective of vertical alignment. In 1978 it was approximately 5 km/h greater. Moreover, on upgrade stretches, in contrast to downgrade stretches, a slight dependence between vertical alignment and speed was apparent. The increased homogeneity referred to above is due to a reduction in the speed of fast PCs above all. It was also established that the sustained speed of passenger cars on upgrades of up to 8 % is below that of 1978 — by as much as 8 km/h on low upgrades. Only in the case of very considerable upgrades was a slight increase in speed recorded. These changes may be explained by the lower speed limits on rural highways.
In the case of heavy vehicles (HVs), the surveys of 1999 reflected a clear tendency towards a lower speed as vertical alignment increases, and thus a clear correlation between those two parameters. The speed distribution for HVs turned out to be slightly less homogenous than that for PCs. Nevertheless, the speed difference between the fast (V85%) and slow, loaded (V15%) HVs has also declined markedly between 1983 and 1999, resulting in more homogenous speed behaviour. The surveys of 2002 showed a slight increase in speed difference on upgrades compared to 1999, while a further reduction was observable on downgrades. In the case of the V15%, which is representative of the crawl speed of loaded HVs, some very large increases were recorded in both 1999 and 2002 compared to 1983.