Research Papers

What the 85th Percentile Doesn't Tell Us: Engineering Safe Roads for Everyone Includes the Other 15 Percent

Filename FINAL-PAPER-37-student-and-CMRSC.docx
Filesize 496 KB
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Date added June 10, 2012
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Category 2012 CMRSC XXII Banff
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Author/Auteur Craig Milligan, Jane MacAngus, Jeannette Montufar


This paper provides insight about the characteristics of higher speed travellers on four-lane divided highways on portions of Manitoba's National Highway System (NHS) - insight which is often lost in aggregate analyses. The 85th percentile speed (the speed at or below which 85 percent of vehicles travel, hereafter V85) is often used in civil engineering actions related to road safety: horizontal and vertical geometry, sight distances, roadside characteristics, and posted speed limits have been set with reference to V85. This paper takes a closer look at the characteristics of groups of higher speed vehicle records (the groups of records at or above the 85th, 95th, and 99.9th percentile speeds) and explores how these characteristics differ from those of lower speed records. The paper looks specifically at the effects of five different factors influencing operating speed: (1) time of day, (2) lighting conditions, (3) season, (4) rain condition, and (5) vehicle type. This is done through: a literature review and an analysis of speed records from three weigh-in-motion (WIM) devices located on Manitoba's NHS roads.

Craig Milligan, Jane MacAngus, Jeannette Montufar