Post on 04-Jan-2016
transcript
Roadside
CE 453 Lecture 23
Sideslopes – Foreslope (Backslope) Design
1. Considerations: Stability and Vehicle Recovery
a. if slope “>” 3:1 use barrier (if in clear zone)b. Hinge Point – minimize to avoid airborne vehiclec. Foreslope – flat enough to allow recovery (4:1 or
less desired)d. Toe of Slope – round to avoid plowinge. Ditch Bottomf. Backslope (3:1 or “less” desired)
2. AASHTO RDG has preferred cross section for two types of channels
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.
Recoverable slopes
motorists are able to stop/slow and return to the roadway safely
1 to 4 or flatter
Recoverable Slope (unless you hit the sign)
<www.geocities.com/Colosseum/Slope/7683/site/highway/10-1.jpg>, February 28, 2002
Non-recoverable, traversable slopesmotorists unable to stop or return to
roadway safelybetween 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
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.
Critical slopes
vehicle likely to overturn
Non-Recoverable Slope
http://ppihc.artemisimages.com/searchres.asp?appmode=detail&id=ppih0750&kw=Scenic&page=1&ec=&collection=&spec=
Roadside – Components
1. Urban Areasa. Curbb. Horizontal Clearancec. Buffer to Land Used. Walkways
2. Rural Areas (focus)a. Clear Zone Conceptb. Drainage Channel Designc. Traffic Barrier Used. AASHTO Road Design Guide (RDG)
Roadside Design Guide
American Association of State Highway and Transportation Officials (2002)
Guide to address design issues off the traveled way (traffic lanes)
Roadside1. Clear Zone (def.) – “The total roadside
border area, starting at the edge of the traveled way, available for safe use by errant vehicles”
2. 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)
Roadside3. AASHTO RDG
a. 30 feet (9 m) – 80 to 85 % recovery
b. Clear zone recommended = f(design speed, ADT, roadside slope, curvature)
c. Compromise between “absolute” safety and engineering, environmental, and economic constraints (always)
Roadside Design Options for Objects
1. Remove (REDESIGN)
2. Relocate
3. Reduce impact severity (breakaway)
4. Redirect by shielding
5. Delineate
But what is an object? signs, poles, slopes
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
Clear Zone
Source: Garber and Hoel
http://epdfiles.engr.wisc.edu/pdf_web_files/tic/other/SAFERcontent_96.pdf
before
after
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
What would clear zone be for same scenario with cut slope instead?
What would clear zone be for same scenario with cut slope instead?
23 feet vs. 30 feet
Why???
Traffic Barriers
Purpose is to minimize severity of potential accidents when vehicles leave the roadway
Prevents vehicles from striking an object such as tree or bridge abutment
Are obstacles themselves (need to consider use)
http://www.southernguardrail.com/p_highway_gr_ar_01.html
http://www.southernguardrail.com/p_highway_gr_ar_01.html