AASHTO TIG Initiative for “Cable Median Barrier” (TIG-CMB)

Information Module Topic Outline

(derived from presentations and notes during July 29, 2005 meeting)

Updated on March 6, 2006

Lead State’s Team and Contact Information

Potential Key Topics within this Module

  • Goals and Objectives
  • Lead State’s Team
  • Related Websites

Goals and Objectives

  • Champion the development of Cable Median Barrier Best Practice Guidelines (CMBBPG) for all State’s who have not yet embraced the Cable Median Barrier technology on their freeways to prevent Across Median Crashes. The CMBBPG is a one-stop-shop where State’s can access all Lead State Cable Median Barrier experiences through the five (5) Information Modules listed below. This format will enable a State to reference any one of the five (5) Information Modules within the CMBBPG during any stage of the Cable Median Barrier decision and installation process as well as providing additional guidance on questions and concerns that arise regarding the Cable Median Barrier Safety Countermeasure.

Background and Problem Identification

Roadway Design Issues

Maintenance Issues

Benefits and Evaluation

System Threats

Lead State’s Team

  • North Carolina

Kevin Lacy(919)

Terry Hopkins(919)

Brian Mayhew(919)

Shawn Troy(919)

Brian Murphy(919)

Roger Thomas(919)

Scott Capps(919)

  • Washington

Dick Albin(360)

  • Ohio

Dean Focke(614)

  • Utah

Rob Clayton(801)

  • Texas

Rory Meza(512)

  • FHWA

Dick Powers(202)

Frank Julian(404)

Joseph Geigle(919)

  • UNC-HSRC

William Hunter(919)

  • AASHTO TIG Representative

Adam Fisher(202)

Related Websites

  • AASHTO Site

  • NCDOT Site

Additional Potential State Contacts

  • OregonDavid Polly
  • WisconsinXiao Qin
  • West VirginiaSarah Daniel
  • CaliforniaJanice Benton
  • IowaTom Welch
  • GeorgiaNorm Cressman
  • IllinoisDave Piper

(Illinois was a lead state in the Midwest States Scanning tour which visited Ohio, Oklahoma, and Texas in September of 2005, and has prepared a report of the Tour. The paper is not yet published. Contact Dave Piper at Ilinois DOT for status of report at 217-785-0720)

Related Analyses Currently Ongoing or Upcoming

  • Revise Chapter 6 of the Roadside Design Guide
  • NCHRP 17-18(3) - Guide for Addressing Head-on Crashes on Freeways
  • NCHRP 22-21 – Median Design and Barrier Considerations for High-Speed Divided Highways in Rural and Urban Areas
  • NCHRP 22-22 – Effectiveness of Traffic Barriers on Non-Level Terrain
  • Texas Research: In service evaluation of Cable Median Barriers in Texas and the comparison versus Concrete Median Barrier
  • Background and Problem Identification - Module 1

Potential Key Topics within this Module

  • Identify the Magnitude of Problem (Crash Analyses)
  • Build Action Plan to Fix the Problem (Compare State to Current AASHTO standards)
  • Convince Peers and Upper Management of the Problem and Action Plan (Sell the Safety Countermeasure)
  • Move Forward with the Problem Solution

North Carolina Information

  • Began looking at the Across Median Crash problem in 1993
  • In 1998 North Carolina began a three pronged approach to prevent and reduce the severity of Across Median Crashes on freeways

Add median protection to freeways with historical crash problems (Phase I)

Systematically protect all freeways with median widths of 70 feet or less (Phase II)

Revise Design Policy to protect all future freeways with median widths of 70 feet or less (Phase III)

  • In 1998 Data analyzed was from 1994 through 1997

Over 1,375 Miles of Full Control of Access Freeway sections were reviewed

Over 10,000 Total Crashes were reviewed

Over 1,000 Across Median Crashes were Identified

For every one Fatal Across Median Crash there were 10 Non-Fatal Across Median Crashes

Across Median Crashes were 3 times more severe than other types of Freeway Crashes

  • 2000 - 2006 TIP included 58 Median Barrier Projects

Approximately 1000 miles of freeway

All Projects have been completed

Initial Projects were over a $120 million dollar investment, not including reoccurring maintenance costs

  • Major catalyst to initiate the 1998 Barrier Program was a section of Interstate 40 near the airport that had Nine (9) Fatal Across Median Crashes in approximately 2 years.

Washington Information

  • In the mid 1990’s WSDOT began using cable barrier to address median crossovers
  • WSDOT considered changes to the median barrier policy in 1994 but decided to wait to see what the NCHRP project would produce
  • In 1999, WSDOT reviewed all cross-median crashes
  • Performed a Benefit/Cost evaluation for each Section. The B/C break was between a 50’ and 60’ median width
  • 50’ median width was a B/C of 4.7:1
  • As a result policy was developed to install median barrier as part of improvement projects on fully controlled access freeways where the median was 50’ wide or less (regardless of crash history)
  • In addition, all sections were prioritized based on B/C (regardless of width)
  • Getting all high priority crash location completed now

Ohio Information

  • Major catalyst to initiate the Barrier Program was a section of Interstate 75 (12-mile section) that had 11 Fatal Across Median Crashes and 14 Fatalities in a 14 month time period.

Constructed in mid to late 1960’s, Six lanes

Tangent alignment, or soft curves

4 foot paved inside shoulders

60 foot median with rounded ditch

6:1 median slopes

65 mph rural highway with urban sprawl (55 mph for large trucks)

95,000 to 72,000 ADT

High percentage of trucks (20 to 29)

  • Political pressures pushed the cable issues
  • 1200 Miles of Freeway Sections (310 miles of 84’ median, 170 miles of 60’ median, 120 miles of 50’ median, and 130 miles of 40 median)
  • Location of interchanges did not have impact on barrier placement
  • Do to randomness of cross median events, a multi-faceted approach recommend

Immediate retrofit at safety hot spots

High Priority – Median width less than 76’ and ADT greater than 36,000

Additional locations – Median width 76’ to 84’ and ADT greater than 26,000 and a crash history

Utah Information

  • Two case studies began Utah’s look into the Across Median Crash problem in 2003
  • Case 1: Interstate 15

2 mile section

110,000 AADT

3 lanes in each direction

36’ median width

Side slopes are 1:6

  • Case 2: Interstate 15

8 mile section

20,000 AADT

3 lanes in each direction

36’ median width

Side slopes are 1:4 and 1:5

Texas Information

  • Crossover crashes were showing up in the media constantly
  • Districts choose the location of barrier placement based on crash history
  • Is currently in the process of constructing 738 miles of Cable Median Barrier, 94 projects at $156 million
  • Also in the process of constructing 85 miles of combination of Cable Median Barrier and Concrete barrier, projects at $30 million
  • To date: 435 miles installed or being installed
  • Using TL-4 in high truck locations

Federal Highways Information

  • Many State DOT’s were unable to identify across median crash locations
  • Information FHWA Knows

Many cross-median crashes occur on medians over 30’ wide

Median encroachments are likely to increase with higher traffic volumes

Cross-over crashes are severe

Median barriers can significantly reduce cross over crashes

Barrier selection and placement are critical for optimal performance

  • Information FHWA Does Not Know

What median width/ADT combinations result in cost-effective warrants?

How should crash history be considered?

How will cable, metal-beam or concrete median barriers perform when struck by a vehicle coming up a slope into the barrier?

When will new warrants be adopted by AASHTO?

Other State’s Information

  • Oregon

Still have the question of ‘Do we handle rural and urban the same?’

Also, ‘When do we close off medians?’

Median widths are typically 70’ to 80’ (pavement edge to pavement edge)

ADT’s go from 30,000 to 150,000

One section installed between Salem and Portland

  • Wisconsin

Criteria is less than 20’ at 20,000 ADT

  • West Virginia

Uses a Frequency and rate Methodology for barrier placement locations

  • California

Median Barrier Placement at 75’ or less

Will investigate locations once they have been identified through a warranting process

Warrants include 0.50 across median crashes per mile per year of any severity, 0.12 fatal across median crashes per mile per year, and a volume versus width criteria

  • Alabama

Warranting Criteria is 2 crashes in a 2 mile section

10 sites have been identified as hot spots

At ADT of 35,000 problems start to occur

  • Iowa

Places barrier in highly dense areas downstream of interchanges

  • Georgia

Has high political pressures from South Carolina

Looks at head on and sideswipe crashes

Criteria is 40’ medians or less

Just put up first 50 miles segment of cable barrier

Program is schedule to protect 50 miles of freeways per year

  • Roadway Design Issues - Module 2

Potential Key Topics within this Module

  • Cable Type (High Tension or Low Tension)
  • Cable Placement – Slope Issues (High Tension or Low Tension)
  • Cable Barrier Design Issues – Guiderail transitions with superelevation, Median hazard guiderail placement
  • Transition from Cable to other Types of Barrier Systems
  • Performance, or more specifically performance from back side hits (through ditch)
  • Test levels (may be a design issue)
  • Anchor crash performance

North Carolina Information

  • Protects all median divided freeways with a 70’ median width or less

Over 1,000 Across Median Crashes were Identified

There was no correlation to speed, median width, volume, time of day, or weather conditions for Across Median Crashes

Potential to eliminate approximately 95 percent of all Across Median Crashes

  • Implemented approximately 500 miles of Low Tension Cable Barrier
  • Low Tension systems have a 11’ 6” designed deflection
  • Cable Barrier not recommended for use on 36’ median width or less
  • Typically have a 4’ offset from ditch line due to potential drainage and maintenance concerns (wet medians, and conflicts with drainage structures)
  • 8’ offset with median widths greater than 60’ (greater the offset from the centerline of median to cable allows for improved mowing operations)
  • Only use on 6:1 slopes or flatter
  • Cable heights for past projects are as follows: bottom cable is 21”, middle cable is 27”, and top cable is 33”
  • Cable heights for present and future projects (2006) are as follows: bottom cable is 20 1/2”, middle cable is 25 1/4”, and top cable is 30”
  • Have all the Roadway Design Specifications and Drawings for median barrier systems in .pdf format that can be attached.

Washington Information

  • Implemented both High Tension and Low Tension cable systems
  • Barrier installation costs are as follows (barrier only)

Generic cable median barrier$8.33 per foot

High Tension Cable Median Barrier$12.23 per foot

W-beam barrier$13.65 per foot

Pre-cast concrete barrier$24.64 per foot

Single slope concrete barrier$44.94 per foot

Cast in place concrete barrier$79.36 per foot

  • Generic cable median barrier has been crash tested in accordance with NCHRP 350 Test Level 3 criteria
  • Cable heights are as follows: bottom cable is 21”, middle cable is 25.5”, and top cable is 30”
  • Uses New York terminal design
  • Uses South Dakota transition design from cable to W-Beam
  • The CASS system is the only High Tension system installed so far for median use
  • Has installed the CASS system with precast concrete sockets, steel tube sockets, and without sockets
  • High Tension systems have a 10’ deflection with a 16’ post spacing
  • Currently have approximately 40 miles of generic cable barrier installed and 70 miles of High Tension cable barrier that is installed or under contract
  • Cable placed on 6:1 slope and a 10’ offset from the edgeline
  • Average installation costs for the generic (low tension) system are $44,000 per mile
  • Have had a concern for anchor movement with one installation of high tension cable barrier

Ohio Information

  • Implemented cable system after a rash of accidents. Decided to use High Tension system. First installation (14 miles) was constructed in 2003
  • Went with High Tension for limited deflection for tight median fits
  • 14 mile segment - Cable placed on 6:1 slope with a 60’ median
  • On first project, cable design to be placed at a 10’ offset from the ditch centerline, ended up being a 14’ to 16’ offset from the ditch centerline due to drainage tiles
  • Designed a non-socketed system, but maintenance is switching to a concrete socked system as posts are damaged
  • Brifen’s TL-3 product used, cable heights are as follows: bottom cable is 20 1/16” and top cable is 28 3/8”
  • 50 miles have been added by the end of 2005 in various parts of the state. Trinity CASS, Nucor-Marion Steel Saferoads, and another Brifen were installed
  • No standards yet, each project is site specifically designed

Utah Information

  • Implemented High Tension Systems
  • Lessons Learned about the Design Process

Median should have a compacted surface

Cable should be offset from water flow to facilitate winter maintenance and avoid erosion around foundations

Concrete foundations (sockets) should be flush with ground to avoid vehicle contact

1:6 is the steepest desirable slope

Systems can sustain hits and remain effective

Offsetting the barrier 6’ to one side appears to have increased the number of hits from that side

  • Has Standard Specifications for Barrier systems, Standard Drawings for Design and Construction, and Research publications on lessons learned
  • Cable pre-stretched and pre-tensioned

Texas Information

  • Implemented High Tension cable systems
  • Only use the High Tension cable systems in median applications
  • Require a deflection of less than 8’
  • Require a 6:1 slope, sometimes has to do a lot of regrading
  • Standard Details and Specifications available from DES-RDS
  • Used all concrete barrier until cable came around
  • Post spacing is 10’ to 20’ from company to company to achieve less than 8’ deflection
  • Uses milled Rumble Strips on many inside shoulders of 4-lane divided roadways
  • Takes the Cable Barrier behind the W-Beam at bridge locations
  • Barrier installation costs are as follows (barrier only)

High Tension (two companies)$12 per foot$4500 per end unit

High Tension (four companies)$9 per foot$2400 per end unit

  • Follows manufactures specifications for each barrier type
  • Always place at the shoulder point, usually 10’ to 12’ off the edgeline
  • Using TL-3 and TL-4 installations
  • Requiring delineation on the posts

Federal Highways Information

  • Working on NCHRP 17-14(2)

Survey State Transportation Agencies regarding median practices

Analyze cross-median crash data from NC

Analyze median involved crash data from CA, NC, OH

Recommend revised median barrier warrant criteria and other median design guidelines

Median barrier warranted up to 70’

Everything up to 50’ – should have a barrier

50’ or less – State will have to show they do not have a problem

Will force States to be proactive

Revise Chapter 6 of the Roadside Design Guide

  • New NCHRP to investigate proper slope placement on non-level terrain

What happens to the cable system going uphill

Analysis is about 2 years out

Other State’s Information

  • Wisconsin

Criteria is less than 20’ at 20,000 ADT

Installing both High Tension and Low Tension cable systems

  • California

Median Barrier Placement at 75’ or less

  • Alabama

Installing Low Tension cable systems (10 miles)

On 50’ median width placed W-Beam on 4:1 slopes at median slope break

Cost $800,000 to regrade 2 miles of median to meet a 6:1 slope placement for cable barrier

  • Iowa

Installed High Tension cable systems

  • Georgia

Installed High Tension cable systems

  • Pennsylvania

Looking at proper barrier placements on slopes

  • Florida

Install barrier on all divided highway medians of less than 64’

  • Maintenance Issues - Module 3

Potential Key Topics within this Module

  • Barrier Hits per Mile
  • Recovery of Maintenance Cost from Drive Away Vehicles
  • Frequency of Repairs to Cable Guardrail
  • Cable Downtime
  • Mowing Concerns

North Carolina Information

  • How to deal with recovery of maintenance costs from drive-away vehicles
  • Discussion of implemented guardrail tagging system to recover state property damage costs from insurance companies
  • Out of 1,592 cable hits there was $955,800 in State Property Damage
  • How to deal with the frequency of repairs to the cable systems in a timely manner
  • How to deal with the mowing issues
  • Retentioning Issues – should systems be retentioned or not? Need to establish procedure for checks and retentioning

Washington Information

  • Low Tension - $2,570 Maintenance Repair Costs per Mile per Year

141 maintenance repairs

Average of 6.7 posts hit

Average of 9.4 hours of repair

Average of $733 of total repair costs

51 percent were matched to crash reports

  • High Tension – CASS with concrete sockets

18 Hits

Average of 5.4 posts hit

Average of $634 of total repair costs

  • Crews initially believed rail required more effort and resisted change. However, after some experience, they showed support for additional installations
  • One crew estimated that 30 percent less time was required than W-Beam Guardrail
  • Cable system requires additional parts to be stocked
  • The system requires additional training
  • No-one has ever been injured while repairing cable barrier
  • Appears to be a cost effective solution to median crossover crashes
  • Does not require excessive maintenance resources and limited concerns are reported by personnel with cable barrier experience
  • Maintenance has some stockpiles of parts but are concerned about the number of different systems

Ohio Information

  • Maintenance Issues drove choice for High Tension cable over untensioned system – the reported performance of tensioned cable after an impact was that the system was ready for another crash
  • On the Brifen socketed system, the line posts concrete foundations came out of the ground after an impact and laid in the median for two and a half months. This was the section where the district forces wished to provide a concrete socket at locations where the driven posts were damaged in an impact. The quality of the concrete and construction techniques may have been questionable. The time delay was caused by frozen median conditions, precluding maintenance from getting in to fix the damaged sockets
  • 5 to 7 hits per mile per year
  • 2 to 5 days to repair from notification (depends on severity)
  • Have mowing concerns (some)
  • Have snow removal concerns (many)
  • Various methods of repair, District forces, Contractor repairs with no parts contracts, and now a Maintenance parts contract

Utah Information