High Tension Cable Median Barrier

March 17, 2011

Cross median crashes

• Cross median crashes are 3 times more deadly than other types of crashes.

• A vehicle travelling at highway speeds can cross a 36’ to 50’ median into oncoming traffic in the time it takes to:– Change the radio station– Answer a cell phone– Yawn

Cross Median Crashes

• Difficult to solve– No specific time of day, week, month or

year– Take place on vertical and horizontal

curves as well as straight and flat sections of roadway

– Various causes• Fatigue

• Improper lane changes

• Inattention

• Medical Emergencies

Patterns Emerging

• Entrance and exit ramps that lead to weaving maneuvers

• Changes in the number of lanes

• Median cross sections

Good News• Research has shown that protective

barrier can prevent most cross median crashes, regardless of the circumstances.

• Goal of Cable median barrier: Contain vehicles in the median once they leave the roadway where they are less likely to involve other vehicles and cause a multi-vehicle crash.

Definition• Cable median barrier is 3 or 4 steel

cables, tensioned and strung on posts.

Office of Traffic, Safety and Technology

Benefits of Cable Median Barrier

• Most versatile and forgiving barrier system available for reducing the severity of run-off-road crashes.– When struck

• Posts break• Cables flex• Absorbs most of the crash’s kinetic energy• Redirects the vehicle along the barrier

• National studies have shown a 96% reduction in fatal cross median crashes.

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Benefits of Cable Median Barrier

• Can be installed on a slope • 4:1 or flatter• Farther away from the traveling public

• Show a substantial reduction in fatal and injury crashes when compared to concrete and metal beam barriers

• Low installation costs

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Minnesota Examples

Office of Traffic, Safety and TechnologyVideo 1

Multiple Hits

Office of Traffic, Safety and TechnologyVideo 2

Placement in Median

Major factors to consider are:• FHWA and NCAC (National Crash

Analysis Center) guidance • Median configuration (slopes,

width, depths, etc)• Future adjacent roadway projects • Maintenance

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• FHWA Approval Letterso “V- ditches”o Approved 0- 4’ down the 1:4 fore slope

with >9-10’ from the ditch bottom

• Most of our median ditches are: o Trapezoidal ditcheso 1:4 foreslopeo Average depth of 2’

FHWA and NCAC Guidance

National Crash Analysis Center (NCAC) Modeling and

Simulation • Over 80 modeling and simulations were

completed

Lateral placement where barrier is likely to capture vehicles Lateral placement where barrier may miss some cases

Vehicle Trajectory Envelope - Normalized

Minimum Upper Cable Height to Avoid Over-rides

Maximum Lower Cable Height to Avoid Under-rides

Cable Heights (Brifen TL4)

Median Profile 4:1 – 60 ft width – 2 ft Depth

Median Placement Criteria

• Direction of majority of lane departureso Place cable on opposite side of median

• Computer modelso Place as far from the travelling public as

possibleo Keep within 6 feet of top of side slope

• Avoid the middle of the mediano Soil ConditionsoMaintenance

Placement In Median

Office of Traffic, Safety and TechnologyVideo 3

Cable Median Installations

Minnesota Data•260 miles installed to date•90-100% Reduction in target K&A’s•Additional 90 miles planned

Study Details• MN’s first 75 miles installed

• 2004, 2005, 2006 and 2007• 24 fatal crashes in the 3 years prior to

installation • 13 fatalities were “target” crashes

• Run off road left• Head on• Sideswipe opposing

• 0.75 miles were excluded from the study because of inaccurate reference points

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Study Results

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13 540

64

162

0 339

60

632

0

100

200

300

400

500

600

700

K A B C PD

Cras

hes

Severity

Cable Median Barrier Target CrashesBefore/After Installation

BEFORE AFTER

13

5

40

0 3

39

05

1015202530354045

K A B

Serious Injuries

All severities

Serious Injuries

Crash Costs

• Fatality (K) = $7,100,000• Incapacitating (A) = $415,000• Nonincapacitating (B) = $137,000• Possible (C) = $91,000• Property Damage (PD) = $12,000

Source: Mn/DOT Office of Capital Programs and Performance Measures (July 2010)

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Study Results

• Property Damage Costs = $5,640,000• 470 more property damage crashes after

(632-162)

• Fatal Crash Costs = $92,300,000 • 13 fewer Fatalities after

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Crash Costs

• 1 Cross median fatality where cable median is installed (unrestrained driver)

• 1 life saved for every 17 miles of installed cable median (annually)

• 77 lives saved to date

Office of Traffic, Safety and Technology

Minnesota Examples

Office of Traffic, Safety and Technology

Minnesota Examples

Office of Traffic, Safety and TechnologyVideo 4

Maintenance• Cable Placement

o Out of the center of mediano Shoulder placement

• Remove turn buckles rather than cut cableo Spaced approx. 1000’o Each installation approx. 1 mile in lengtho 5 Opportunities to loosen cable per

installation

• Cable cannot be re-splicedo Maintenance can take up to 6 weeks

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Extrication Difficulties

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Maintenance Training

• How to get slack in cableoManipulate cable (tow service)o Posts – take out or cuto Turnbuckle

• Loosen • Remove• Cut

o Spreader Bar• For woven systems• $300 from manufacturer

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Maintenance Training• Stock piles of parts

oMultiple shopsoMultiple manufacturers

• Steamers to remove posts in ice• Training video on cutting cable• Communication

o First respondersoMaintenanceoDesign

oLocation of turn-arounds

Office of Traffic, Safety and Technology

Office of Traffic, Safety and Technology

Minnesota Links• MN Office of Traffic, Safety, and Technology (OTST)

– http://www.dot.state.mn.us/trafficeng/safety/index.html

• Solicitations– Greater MN & Metro Announcements & Applications– http://www.dot.state.mn.us/trafficeng/safety/hes/index.html

Contact Information

• Julie Whitcher

• 651-234-7019

• Julie.Whitcher@state.mn.us

• MN Office of Traffic, Safety, and Technology (OTST)– http://www.dot.state.mn.us/trafficeng/safety/index.html

Office of Traffic, Safety and Technology