The German Road Traffic RegulationsRoad traffic regulations (StVO) (BMVBS Straßenverkehrsordnung. Dortmund: Verkehrsblatt-Verlag, 2013) stipulate that the driver must choose his speedSpeeds according to the sight distance conditions. If this legal standard were to be observed, the existingSight distanceexisting sight distance would be a good way of influencing speedSpeeds behaviour. However, measurements and observations of the relationship between sight distance and speedSpeeds show that existing sight distance has only a limited effect on the choice of speedSpeeds. The following reasons can be given for this:
Distances and speedsSpeeds are difficult to estimate, especially while driving.
At lower speedsSpeeds, the actual braking distancesBraking distances are underestimated. On fast-traffic highways and motorways, speedsSpeeds are underestimated.
Emergency braking before sudden and unexpectedly occurring obstacles are rare events. The driver has no feeling for the forces involved.
As a consequence, the road design is based on the assumption that sight distance has a significant influence on traffic safety, performance and driving comfort and that it must be guaranteed as a design parameter. In order to achieve this, sight distance analyses are required already at the design stage. By reducing the driving space to only one dimension, the geometric sight distance is obtained. The minimum requirement is to check that the geometric sight distance (sight distance plan) in the driving space corresponds to the stopping sight distance required by the driving dynamics depending on the design classDesign classes.
Basically, the most important design principle for the alignment of motorways and country roads is that a vehicle travelling alone can stop safely at any time when the road is wet and clean in front of a suddenly appearing obstacle. Since the required stopping distances are strongly dependent on the speedSpeeds driven, design class-dependent values must be set for the speedsSpeeds driven. On motorways, the recommended speedRecommended speed of 130 km/h is used for this purpose, unless speedSpeeds limits are known in advance (e.g. on regional or urban motorwaysUrban motorways). In this case, these can be used. On country roads, the required stopping distance is based on the planning speedPlanning speeds.
Sight Distance
Road Planning - Freeways and Country Roads ; Chapter : 15 ; 229-238
2022-11-30
10 pages
Article/Chapter (Book)
Electronic Resource
English
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