Abstract
The main objective of the present paper is to investigate the influence of the longitudinal inclination of grades on the speed behavior on highways. For assessing this dependence, all uphill and downhill highway sections were considered separately in the two travel directions and the mean values of both 85th and 15th percentile speeds were calculated for each section. In order to take into account the free speed selection, all speed limited highway sections were excluded from the study. To investigate the speed changes as a function of the longitudinal inclination, the speed differences V85 between the speeds at the end and the beginning of each individual ascending and descending section were calculated as well. The dependencies were assessed also using the “moving average” over the grades. Both methodological approaches show that the magnitude of the longitudinal inclination on uphill sections has a clear influence on the speed and on the speed differences. A significant reduction of the speed and a significant increase of the speed difference were established on ascending sections with slopes over 4%. Furthermore, it was found that the length of the ascending grades also affects the speed differences ΔV85, which increase considerably on longer uphill sections.
Highlights
Driving behavior can be understood as a uniform multi-layered control system, which in road traffic is referred to as Driver-Vehicle-Road ([1], [2])
As stated in previous research, it has been confirmed in this study that the magnitude of the longitudinal inclination has a considerable effect on the speeds V85 and V15 on ascending grades
For gradients above 4%, higher speed reductions and higher speed differences ∆V85 have been detected, compared to those at gradients below 2%
Summary
Driving behavior can be understood as a uniform multi-layered control system, which in road traffic is referred to as Driver-Vehicle-Road ([1], [2]). This system is an ordered classification of influencing variables on the driving behavior. The increased fuel consumption on uphill sections at large longitudinal slopes leads to an increase in drivers' costs and results in higher pollutant emissions. It is necessary to determine an optimal longitudinal slope and an optimal length of ascending sections to ensure a homogeneous driving behavior through a relative constant speed level, to reduce road users’ costs and to lower the pollutant emissions
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