This effort to determine how to measure and evaluate the effects of the geometric elements in the operation of vehicles encroaching in median and border areas, considers the frequency and nature of vehicle encroachments on roadside areas, and the standards of measure. Reference is made to research, and the variables to be considered in overall encroachment frequency, spot frequency and nature of encroachments are listed. Studies in Illinois led to the conclusion that a 30 ft. width of obstacle free median with mild cross slopes is the absolute minimum requirement for the relatively safe stopping or control of vehicles encroaching on medians at rural operating speeds. Roadside obstacles and their relation to encroaching vehicles are discussed as well as warrants for the installation of median barriers and guardrails. Because the accident frequency associated with any one obstacle is so small, the probablistic approach is the best method to identify hazardous roadside situations on a large scale. It is recommended that 2 standards be used to measure and evaluate a section of highway with respect to operational effects of secondary stopping and recovery areas. The first standard is encroachments per mile per year. The ratio, encroachments per accident should be used as a measure of the "forgiveness" of the secondary stopping and recovery area.

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    Transportation Research Board

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  • Publication Date: 1976-12

Media Info

  • Media Type: Digital/other
  • Features: Figures; References; Tables;
  • Pagination: 12 p.
  • Serial:

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Filing Info

  • Accession Number: 00148112
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Feb 16 1977 12:00AM