Research was needed in the field of determination of clearance of vehicle motion and of transverse clearance between various travelers on roads - with and without opposing traffic - depending on passing speed, lane width, shape and clearance of lateral obstacles, taking into account the dimensions of current vehicles.
The objective of the project is a development of scientific fundamentals for a possible revision of the geometric standard SN 640 201. Project is also aimed on determination of statistically secured dimensions of the speed dependent dimensioning elements of the standard profile of cross sections based on empirical data.
The examination procedure includes the following steps:
Phase 1: analysis of predictors, Requirements for measurement sections, evaluation of measurement sections, testing measurements, statistical surveys.
Phase 2: Measurement series roads outside cities, measurement series streets in town, measurement series outside the roadway area.
Phase 3: Determination of contexts, derivation of reference values, standard proposals, reporting.
The statistical analysis of the Swiss vehicle fleet yielded approximately 5 cm greater vehicle widths than in the existing standard for passenger cars (PC) as well as heavy goods vehicles (HGV).
The speed dependence of the range of lateral movement and the additional space for oncoming or overtaking traffic, as it is contained in the existing standard, could in principle be confirmed through empirical measurements. There were found some considerable differences between the measurement results and the reference values of the standard (cf. illustrations). Moreover, the results show that it is necessary to distinguish between the categories PC and HGV for the derivation of the range of movement and the additional space for oncoming or overtaking traffic. The equality of the additional space for oncoming traffic and the additional space for overtaking, as it is contained in the existing standard, is not correct. In addition to this, the available lane widths as well as elongated obstacles next to the road do affect the size of the design elements. Furthermore the examination has shown that the passing distances to overtake bicycles determined empirically correspond to the existing standard values for the speed range of 30 to 50 km/h. However, the sample size was restricted at the measurements on hand.
From the analyses the following conclusions arose:
Regarding the basic dimensions of PC and HGV it was determined that the vehicle widths have increased within the last few years. Still remains to be checked how such increase might change the existing standard values.
There are considerable differences between the results of the measurements and the reference values in the standard. Even though, the speed dependence of the design elements of the standard profile was confirmed. Moreover, the research showed that there should be two categories of speed-dependent design elements. It has to be distinguished between the categories PC and HGV.
The measured ranges of movement depending on the driven speed are for PC approximately 10 to 15 cm and for HGV approximately 5 to 10 cm bigger than in the existing standard. The additional space for oncoming traffic is approximately 40 to 70 cm (PC) and approximately 20 to 35 cm (HGV) bigger than in the existing standard. On normal wide lanes the additional space for overtaking on highways is considerably smaller than the additional space for oncoming traffic at comparable speed levels. The differences are approximately 40 cm