The Traffic Accident Reconstruction Origin -ARnews-
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The Traffic Accident Reconstruction Origin -ARnews-
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(1) Not all roads are designed. Many just "evolve" over the years from a pedestrian path to a wagon trail to someone covering it with gravel to someone paving it and agreeing to maintain it. These roads (sometimes called farm to market roads) have no design standards to meet. Therefore, they meet no "design standards" for stopping sight distance. As such, typical operation at a reasonable speed to stop for existing conditions rests with the driver(s). We're not speaking of sand storms or sheeting rain, just normal day-to-day operation.
(2) Roads that are designed or improved in sections are typically meant to be operated at particular speeds and road slopes and it's curvilinear nature are considered in the design and building process to allow for safe operation under typical conditions at some speed. This study would include stopping sight distances based on design standards that build in comfort distnaces with lower friciton values and longer perception/reaction times.
Design manuals, like AASHTO, show how to determine via measurement the "design" stopping sight distance. You can measure any roadway as to how far you can see, and compute what friction demand and PRT are necessary to stop under those conditions. However, applying standards for designed roads is not usually applicable.
Research on accident hx., speed studies, volume studies, etc. yield a fuller picture than trying to force design standards on any non-designed piece of roadway. Reasonable speeds for obvious conditions is the key.
Ed
Ed Phillips
edphill@aol
For example, to continue this discussion look for a thread titled
stopping sight distance
If this thread does not exist in the current archive, you can begin another one by using that title.