ASK THE EXPERT Frequently Asked Questions. Q.What Is the Safety Edge?
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Transcript of ASK THE EXPERT Frequently Asked Questions. Q.What Is the Safety Edge?
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ASK THE EXPERTFrequently Asked Questions
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Q. What Is the Safety Edge?
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Q. How does the Safety Edge compare with conventional asphalt paving processes?
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Q. Has the Safety Edge design been used for concrete pavement?
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Iowa PCCP Safety Edge
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Q. My State wants to do a Safety Edge project with an Open House so
interested DOT personnel, local agencies and contractors can observe an installation. Can we get a loaner shoe and technical assistance in planning and presenting information?
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Q. How should a State DOT or local agency select the best site for a Demonstration Project?
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Selecting a Demonstration ProjectFor Your First Project
• Existing edge drop-offs OR minimum 2” overlay
• Progressive district/county• Cooperative contractor• Near central office• Recoverable area beyond
pavement edge• Rural, higher-speed road• Narrow or no shoulders
For an Open House
Important:• Longer project (mileage)• Located near a conference
roomOptional:• Warm-mix asphalt or other
innovation• Easy travel location
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Q. What is the minimum lift thickness that merits the use of the Safety Edge?
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Lift thickness does not correlate with edge depth.
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Q. If a project has paved shoulders, is the Safety Edge needed, and if we have rumble strips do we need it?
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About 40% stopped within 10 feet
About 80% stopped within 30 feet
6-12
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An edge rut is different from a drop-off. Usually this type of rut is from agricultural equipment running on the shoulder.
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Aggregate shoulders can have settlement and over time result in a drop-off or an edge rut.
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Aggregate shoulders in a tangent section perform better than sod shoulders since the shoulders resist water and wind erosion better. However, routine maintenance is still required, which often can become a compromise in tough budgets.
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Q. What if the graded material adjacent to the pavement slopes is greater than the Safety Edge?
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Q. What are other alternates to the Safety Edge?
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Simulation Cases• Edge designs
– 18 edge configurations including bothlimited dimensions and wide wedges
• Vehicles selected– 2 passenger cars, 1 pick-up truck, 1 tractor semi-trailer
(loaded and unloaded configurations)
• Driving conditions– 2 friction conditions to simulate dry and wet roadway
• Driver’s reaction– 3 levels of steering and braking reaction times
Height
Inclination
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Safety Design Criterion D
Geometric criterion:
with the edge drop off height (in)
and the edge slope angle (rad)
3H
D
H
Height
Inclination
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Dcrit
Saferecovery
maneuvers
Failed recovery
maneuvers
Wedge geometries D60°/4” 3.4860°/6” 5.2260°/8” 6.9645°/4” 8.26
Wide wedge (case 1) 8.660°/10” 8.71
Wide wedge (case 2) 9.260°/12” 10.4545°/6” 12.3845°/8” 16.51
45°/10” 20.6445°/12” 24.7730°/4” 27.8730°/6” 41.830°/8” 55.73
30°/10” 69.6630°/12” 83.620°/7” 164.58
DcritDcrit
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Conclusion
• For passenger vehicles, wedge is safely designed under all kinds of driving conditions if: D ≤ 10.4 in
• For all types of vehicles (including heavy commercial vehicles): D ≤ 3.5 in
Dcrit (in)
Mirage 16.5Camry 10.4
Pickup truck 24.8Tractor semi-trailer 3.5
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Q. Will the wedge shape increase erosion or cause aggregate to slide away?
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Before Photos
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After Photos–Six Months After Paving
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Q. How much width does the wedge add?
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Q. What happens when you come to a driveway?
http://fhwa.na3.acrobat.com/sedriveways/
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Q. What happens when a future resurfacing project comes, will the pavement be much wider?
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Q. How do you pave under the guardrail with the Safety Edge shoe attached?
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Q. This looks to be simple. Can we make our own device, and how difficult is it to install the manufacturer’s shoe?
http://fhwa.na3.acrobat.com/seshoeinstall/
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Q. When you are doing a project with double lifts, do you need the Safety Edge for both lifts?
http://fhwa.na3.acrobat.com/seddlift/
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Every Day CountsInnovation Initiative
Contact InformationFor training or more information on this Every Day Counts Initiative,
please contact your local FHWA Division Office.
To learn more about EDC, visit:
http://www.fhwa.dot.gov/everydaycounts
Contact InformationFor training or more information on this Every Day Counts Initiative,
please contact your local FHWA Division Office.
To learn more about EDC, visit:
http://www.fhwa.dot.gov/everydaycounts