The speed on roads describes the driving behaviour and therefore is a fundamental value of design standards. On the one hand the speed models of the existing standards (VSS) are based on physical calculations and on the other hand on speed measurements. Latter stated values are used to compare with the models. The driving speed was mainly affected by the geometry of the roads as well as of the speed limits. Furthermore the speed of heavy vehicles affects the overtaking behaviour essentially. This manifests mainly at upgrades and downgrades, where the speed of heavy vehicles is much lower than the speed of the passenger cars. This is why the real driving behaviour of vehicles on upgrades and downgrades is repeatedly measured in the past. After the year 2005 the allocation of heavy vehicles with weights above 28t are no longer applicable. So it must be assumed that the percentage share of drives with commercial vehicles increased essentially since the year 2002. Accordingly the question at which standard the speed of heavy vehicles in upgrades and downgrades has levelled off must be stated.
The aim of this research project is to review respectively update the speed on upgrades and downgrades, which were surveyed in the year 2002. Therefore the surveys of traffic flow on motorways and rural roads were analysed for heavy vehicles with gross vehicle weight above 28t after the repeal of allocation, so that the results of this investigation can be compared to previous results. The priority is the crawl speed of slow and heavy loaded vehicles which travels without hindrance at the end of a sufficient long upgrade stretches at different gradients. To verify the effects at drives of heavy vehicles for the no longer existing allocation of weights above 28t, corresponding weight in motion (WIM) measurements were analysed. The WIM should be executed primary for the transalpine north-south-traffic.
In the study, the following steps are provided:
Step 1: Speed measurement location providing
Step 2: Evaluations
In this step, the velocity profiles along the slope distances are determined and examined the relationship between duration and size of the pitch speeds. Is also included the evaluation of weight measurements at the decisive WIM measuring points of ASTRA
Step 3: Comparison with readings 2002
The aim of the study is the comparison of any possible rate changes between the states in 2002 and today and the assessment of the impact on traffic flow.
Step 4: Reporting
For the appraisal of the homogeneity respectively the statistical spread of speed, the speed difference between fast (V85%) and slow, loaded (V15%) heavy vehicles were regarded. In addition the standard deviations of average speeds at each last cross section of the gradient were considered. The speed difference between faster (V85%) and slower (V15%) vehicles reveals only a small change, compared to the states between 2002 and 2009. For all values the average speed differences are at 1.7 km/h for upgrades and at 1.0 km/h for downgrades. Equally the standard deviation of the average speed VM reflects a small change for upgrades (0.1 km/h) and downgrades (1.1 km/h). It follows altogether that the homogeneity of the speed distribution has not changed. The speed profiles along four upgrades stretches prove that the dependence between distance and loss of speed in 2009 were similar to that in the year 2002. The comparison of V15% at the beginning and the end of upgrades expose for the year 2009 as well as for the year 2002 a deceleration of the speed exclusively. The decreases of speed at the single upgrades stretches viewed at both periods under observation have similar ranges, in the year 2009 between 5 to 17 km/h and in the year 2002 between 5 to 24 km/h. In 2009 at three of six comparable stretches the crawl speed of slow, loaded heavy vehicles (V15% - values) at the end of upgrades increased up to 6 km/h and reduced for two stretches up to 4 km/h. Only small changes in average speeds have revealed in 2009 (47.5 km/h) and 2002 (46.7 km/h) at all comparable routes. As in previous investigations recognized, the tendency of declined crawl speed with increasing gradient persists in 2009 also. The comparison of the determined functions of the states “before” (2002) and “after” (2009) reflects small differences. The carried out investigation performed for reflect the changes in the direction of the gradient shows no significance from the statistical point of view. That is, the abolition of the allocation of heavy vehicles with weights above 28t does not cause adequate changes in the crawl speed of heavy vehicles in upgrades. As a result of the dosage measures, started at the beginning of the year 2002, a decrease for the number of transalpine heavy vehicles drives was revealed. This reduction was apparently compensated by heavier operating weights per drive. Within the scope of the available weight evaluations and comparisons, tendencies to higher operating weights after the allocation of total
Actualization of the speed upgrades and downgrades.