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Roadside

Roadside. CE 453 Lecture 23. Sideslopes – Foreslope (Backslope) Design. Considerations: Stability and Vehicle Recovery if slope “>” 3:1 use barrier (if in clear zone) Hinge Point – minimize to avoid airborne vehicle Foreslope – flat enough to allow recovery (4:1 or less desired)

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Roadside

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  1. Roadside CE 453 Lecture 23

  2. Sideslopes – Foreslope (Backslope) Design • Considerations: Stability and Vehicle Recovery • if slope “>” 3:1 use barrier (if in clear zone) • Hinge Point – minimize to avoid airborne vehicle • Foreslope – flat enough to allow recovery (4:1 or less desired) • Toe of Slope – round to avoid plowing • Ditch Bottom • Backslope (3:1 or “less” desired) • AASHTO RDG has preferred cross section for two types of channels

  3. Source: A Policy on Geometric Design of Highways and Streets (The Green Book). Washington, DC. American Association of State Highway and Transportation Officials, 2001 4th Ed.

  4. Recoverable slopes • motorists are able to stop/slow and return to the roadway safely • 1 to 4 or flatter

  5. Recoverable Slope (unless you hit the sign) <www.geocities.com/Colosseum/Slope/7683/site/highway/10-1.jpg>, February 28, 2002

  6. Non-recoverable, traversable slopes • motorists unable to stop or return to roadway safely • between 1:3 and 1:4 • recovery area must be to the toe of the slope and a clear runout area at base with 1:6 or flatter slope

  7. Source: A Policy on Geometric Design of Highways and Streets (The Green Book). Washington, DC. American Association of State Highway and Transportation Officials, 2001 4th Ed.

  8. Critical slopes • vehicle likely to overturn

  9. Non-Recoverable Slope http://ppihc.artemisimages.com/searchres.asp?appmode=detail&id=ppih0750&kw=Scenic&page=1&ec=&collection=&spec=

  10. Roadside – Components • Urban Areas • Curb • Horizontal Clearance • Buffer to Land Use • Walkways • Rural Areas (focus) • Clear Zone Concept • Drainage Channel Design • Traffic Barrier Use • AASHTO Road Design Guide (RDG)

  11. Roadside Design Guide • American Association of State Highway and Transportation Officials (2002) • Guide to address design issues off the traveled way (traffic lanes)

  12. Roadside • Clear Zone (def.) – “The total roadside border area, starting at the edge of the traveled way, available for safe use by errant vehicles” • Concept – area should be as wide, flat, and rounded as practical and as free as practical from physical obstructions (want a driver who leaves roadway to regain control and return to the roadway)

  13. Roadside • AASHTO RDG • 30 feet (9 m) – 80 to 85 % recovery • Clear zone recommended = f(design speed, ADT, roadside slope, curvature) • Compromise between “absolute” safety and engineering, environmental, and economic constraints (always)

  14. Roadside Design Options for Objects • Remove (REDESIGN) • Relocate • Reduce impact severity (breakaway) • Redirect by shielding • Delineate But what is an object? signs, poles, slopes

  15. Clear Zone • Unobstructed, relatively flat area beyond the edge of the traveled way • Provides area for vehicles to recover • Width depends on: • Volume • Design speed • Slope of embankment • Measured from edge of pavement to nearest • Obstacle (tree, telephone pole, etc) • Steep slope, non-traversable ditch • Cliff • Body of water http://www.storycounty.com/engineer/roadside_safety.htm

  16. Clear Zone Source: Garber and Hoel

  17. http://epdfiles.engr.wisc.edu/pdf_web_files/tic/other/SAFERcontent_96.pdfhttp://epdfiles.engr.wisc.edu/pdf_web_files/tic/other/SAFERcontent_96.pdf

  18. after before

  19. Iowa’s Roadway-Related Fatal Crashes • 52% of Iowa’s fatalities are related to Lane Departure • 39% of Iowa’s fatal crashes are single-vehicleRun-Off-the-Road (ROR)crashes

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