Best Practices A comparison of Mobile Barriers MBT-1

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Best PracticesA comparison of

Mobile Barriers MBT-1

& Caltrans Balsi Beam

Mobile Barriers would like to thank The FHWA Office of Safety

for their review and comments prior to finalization of this comparison.

Mobile Barriers would also like to thank members of Task Force 13

the joint subcommittee ofThe Associated General Contractors of America (AGC)

The American Road & Transportation Builders Association (ARTBA) &The American Association of State Highway and Transportation Officials (ASSHTO)

for their thoughts and comments.

Basic Comparison

Mobile Barriers MBT-1 Caltrans Balsi BeamTested:

• MASH TL-3 No• NCHRP 350 TL-3 TL-2 (w/ issues)• FHWA Reviewed Yes No• FHWA Acceptance/Eligibility Ltr Yes No

Impact Severity Tested 150 kJ (110,600 ft-lbf) 19/66 kJ (13,700-48,800 ft-lbf) (for context, standards for NCHRP 350 TL3 Pickups & TL-4 Straight Trucks ranged from 132-138 kJ)Barrier

• Work Area 20-80’ 20-30’• OAL 40-100’ 40-50’• Barrier Height 5’ 3’ • Weight 50,000 lbs est. 20,000 lbs

Tractor Any Standard Tractor Specially Modified Tractor Required

Mobility/Moving Ops Fully Mobile Immobile (tractor locked/jack stands down)

Time to Deploy/Remove (min) 0 (park & work) 20 Min (lock tractor, drop jacks, rotate arms)(inherent danger/vulnerability)

Mechanical Problems Nothing Material Lock Up on Setup/Removal(arms lock in rotation and extension )Bolt Sheer & Other Issues also reportedTest issues - old vehicles, snagging, exit

Features/Options 20’ Decks & Lockable StorageOnboard Power, Air & LightsSignage & TMA

Cost Significantly Less & Modular

Larger

Compare Balsi Beam• Small enough to enclose (short or extended)• Half the height (3’ vs 5’)

MBT-1… Taller/Heavier/Stronger

Shoulder vs Waist High

MBT-1… Better Physical & Visual BarrierTraffic cant see in (better traffic flows)

Crews can still see out

BalsiLess Physical &

Less Visual Barrier

MBT-1… On-board:• Power - 120/240, solar & batteries, • Air – enough for jackhammer, impact wrenches & tools• Lights – great lighting – better than traditional 4 head arrays (ASSE study)• Storage – lockable storage & 20’ decks for materials & supplies • Signage & TMA (typically TL-3)

MBT-1 in the Real World – After 2 Semi Truck HitsMinor damage ($2000 & scratches)

Both trucks ran down, along and off the wall under control (one drove on/one stopped)

Semi impact… higher than Balsi wall

MBT-1 Turns and Redirects Cleanly (MASH TL-3: 5000 lbs/63 mph)

MBT-1Fully Operable After Crash

Balsi – Jammed

MBT-1 … clean – no snagging – extra wall height helped control impact(MASH TL-3: 5000 lbs/63 mph/25°)

Balsi - Snagging (@ only TL-2: 4000 lbs/43 mph/25°)

(Report says 1.5 degrees)

Balsi - Snagging (only TL-2 @ 44 mph/21°)

MBT-1TL-3/63 mphImpact Severity: 150 kJ

BalsiTL-2/43 mphImpact Severity: 66 kJ (pickup)

19 kJ (car)

MBT-1 … BalsiSide by Side

MBT-1TL-3/63 mphImpact Severity: 150 kJ

No Snagging

BalsiTL-2/43 mphImpact Severity: 66 kJ (pickup)

19 kJ (car)

Snagging

MBT-1… Modular(repair/replace only what’s damaged)

Repair/Replacement

Balsi ... Not Modular

Replace a Balsi? $675,000

Replace: a Wall? $25,000

a Caboose? $55,000or a Platform? $75,000

Fixed vs Articulating WallAdvantage or Detriment?

MBT-1Theory: Stronger, Simpler & More Efficient

BalsiTheory: Crews Can Work Either Side

In Practice: Crews Don’t… Becomes Detriment Crews Plan Work & Work Zones Setups

Lock, Align, Extend & RotateAdds 20 min of Hazardous Setup

Each Arrival/Departure – Each SiteOn Road/In Traffic/In Work Zone

Most Dangerous Location to ConfigureSingle Beam only 24” High – Real Risk of Penetration

Complexity adds to Lockup/Failure & Decreases StrengthLockup Compounds Danger – Joints Decrease StrengthVulnerability adds Danger for Crews & Passing TrafficComplexity Adds Cost to Build, Operate & Maintain

$675,000

In Practice: Exactly That… Pull In & WorkSimple to Operate & Maintain

Crews Plan Work & Work Zone SetupsEasily Reconfigured to Right or Left when Necessary

All Configuration Out of Traffic In Secure Area(30 min or less when familiar)

Rigidity Adds to StrengthSimplicity allows for Storage, Lighting, Power & Air

Simplicity Allows for More Economical PriceEasier to Build & Maintain

Half the Cost (or Less) & Modular

MBT-1… Easily reconfigured for Right or Left workdepending on end to which tractor is attached. Tractor can attach at either end.Rear Axle Assembly (“Caboose”) moves and attaches to end opposite tractor.

For animation of reconfiguration, see “Reconfiguration” page at www.mobilebarriers.com

Balsi … TL-2 onlyCrash Rpt Recommendations (pg 31)

“It is recommended that the [Balsi] be outfitted with a truck-mounted attenuator (TMA) and followed with a shadow vehicle that also has a TMA. This is recommended because no testing was done on the [Balsi] to ensure that a rear hit on a deployed system will not collapse the system.”

But…

Balsi Flier (No-Boundaries)…no TMA

TMAMBT-1 … TL-2 or TL-3 (real world speeds - real world impacts)

Balsi …TL-2 onlyCrash Rpt Recommendations (pg 31)

Use limited to locations where “the potential for vehicle impacts to not exceed Test Level 2 conditions (i.e. under 70 km/h (43 mph).”

TL-2 at Interstate Speeds??

Using TL-2 TMA’s for Interstate Work? CA is one of few that still does.

Most don’t.

Typical Interstate Speeds exceed 43 mph TL-2 levels

(and are rarely posted down to that level)

MBT-1 … TL-2 or TL-3 (real world speeds - real world impacts)