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Andy Keel, P.E.Roadway Design OfficeCriteria and Standards Section850-414-4334/SC 994-4334andy.keel@dot.state.fl.us
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Do Cable Barriers Work?
Design Conference 2006
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Do Cable Barriers Work?
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DISCLAIMER
PREFERENCES
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OUTLINE• Why Median Barrier?• Old vs. New• High Tension Cable Barrier System• Design Considerations• Construction Sequence• Maintenance• Installation Cost• Cable Barrier In Florida• Things To Think About
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Design Conference 2006
Why Median Barrier ?
• Many Cross Median Crashes occur on medians greater than 30 feet wide
• 64 Ft. Median – 30 Angle – 70 mph
• Across Median Crashes 3x’s more severe than other freeway crashes (NC98)
• WI Study- 53% of Cross Median Crashes resulted in personal injury & 7% involved a fatality
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Why Median Barrier ?
• Median encroachments increase with higher traffic volumes
• Brevard Co. 1994-2001 – 123 fatal crashes. Almost 1/3 involved in median crossovers
• Crossover deaths may be under reported because of the way reporting officers record the incidents on crash reports
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Why Median Barrier ?
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446342118Fatalities
425261712Fatal Crossover Crashes
20052004200320022001SR 91
Florida's Turnpike Median Crash Data
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Median Barrier Options Available
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Median Barrier Options Available
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Median Barrier Options Available
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“We Don’t Do Cable”
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Cable
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Memo
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US Cable
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US Cable
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US Cable After Hit
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High Tension Cable After A Hit
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Basic Segments Of Cable Barrier System
• End Anchors
• Transition Sections
• Basic Length of Need Section
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End Anchors• Deadman Type
• Crashworthy
• Guardrail
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Deadman Type
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Crashworthy
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Guardrail
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Transition Section
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Basic Length of Need Section
• Brifen
• CASS by Trinity
• Gibraltar
• Nucor Marion
• Safence
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Brifen
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CASS
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Gibraltar
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Nucor Marion
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Safence
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Tension Adjustment
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Design Considerations• Location
• Deflection Space
• Type Anchors
• Post Footings
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Design Consideration• Location- Center Line Of Median
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Design Consideration• Location- Shoulder
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Design Consideration• Location – Slope
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Design Consideration• Location – Slope
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Design Consideration• Location – Slope
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1 ft. Offset 4 ft. Offset
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Design Considerations• Deflection – Controlled by Post Spacing
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Design Consideration• Deflection – Also affected by angle & speed
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Design Considerations
• Deadman
• Crashworthy
• Guardrail Connection
Type Anchors
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Design Considerations
Driven Concrete With SocketsPost Footings
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Construction SequencePrepare Ground
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Construction Sequence
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Misc. Asphalt Placed
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Construction Sequence
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Holes Drilled & Sockets Installed
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Construction SequencePosts Installed and Cable Strung
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Construction SequenceCable Tensioned
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Maintenance
• Remove Damaged Posts
• Insert New Posts In Sockets
• Re-attach Cable
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Maintenance Video
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Maintenance
Estimated Repair Time For A “Typical Hit”
Most States reporting 30-60 Minutes
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Installation CostsNumbers Vary
Anchors Included or separate?
Cable System Only?
Mowing Strip / Earthwork?
Maintenance Of Traffic?
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$9 --- $19 LF
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Installation CostsBeachline Comparison
6.3 mi. Double Face Guardrail
11.1 mi. Cable Barrier
$338,000 per mi.
$209,000 per mi.
Savings: $129,000 per mi.
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Cable Barrier In Florida• HEFT
• District 7
• Turnpike Canals
• District 1
Developmental Specification
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Things To Think About
We Know:
Median barriers can significantly reduce Cross Median Crashes
Barrier selection & placement are critical for optimal performance
Cable barriers offer cost savings while meeting current test level requirements
High Tension Cable barriers can sustain hits and still remain effective
Number of incidents will increase, but severity will be significantly reduced
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Things To Think About
We don’t know:
What median width / ADT combinations result in cost-effective warrants
How median barriers (cable, w-beam, concrete) perform when struck by a vehicle coming UP a slope into the barrier
Life cycle cost
Performance in hits on convex side of horizontal curves
Performance in sag vertical curves
Life of the cables / long term performance of cables
$$$$$
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Things To Think About
Additional Issues:
•Ambient air vs. rope temperature
•Cable tension tolerances
•Best lateral placement
•Pre-stretched vs. non pre-stretched
•Field applied vs. factory applied fittings
•Others ??
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Things To Think About
The future:
Standardization?
Standardization of testing?
Standard specification?
?
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Snow At Concrete Barrier
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