You shouldn’t have to try to decipher a spec sheet written in a language you don’t speak when selecting a TMA crash cushion. However, this is how many contractors do it, check some brochures, choose whichever seems the most impressive, and pray it is.
This guide avoids the jargon and provides you with a real decision filter, a step by step filter that gets you to the right unit, rather than just a unit.
Don’t Begin with the Product Catalog; Start With Your Road Speed
The one mistake that you can make with a crash cushion is to go with one that you can find at a lower price instead of what you actually need.
Flip that order.
Don’t judge the actual speed at which your road operates before you even view a single product page, drivers will consider this more of a suggestion than a rule.
A quiet service road, which runs at speeds of 50-60 km/h, has very different protection requirements from a road such as Sheikh Zayed Road or Emirates Road, which are within 50m of the cliffs and drive close to 100 km/h or more.
Test Level 3 units, also known as TL-3, are the lowest tier of tests, for high speed work zones, typically those with speeds of 55 mph or greater (90 km/h). Faster speeds can reasonably be justified in using a TL-2 class, typically at a significant cost advantage.
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If you miss this step, then all the other steps below pick up the error.
Determine if Work Is Stationary or Moving
The next fork in the road is not as complicated as it sounds—are you stuck in one spot or are your men moving down the road as work goes on?
Static jobs, such as bridge joint repair, or repair of a fixed pavement section, require a unit to remain fixed over the entire life of the job.
Jobs that have to be moved, such as lane striping or debris sweeping, require a unit to be shifted back and forth from a shadow vehicle to keep at least one safety zone in front of the crew.
Shadow vehicles are used specifically when a vehicle is intruding into a work crew and are on foot, but also to minimize the impact that the vehicle has on a work vehicle when it collides with a work vehicle.
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A fixed-position unit for mobile work or vice-versa is a mismatch, which becomes evident when the job begins.
Match the TMA Crash Cushion Type to How a Vehicle Might Hit It
However, not every impact occurs head-on, and Truck Mounted Attenuators crash cushions are designed with this in mind.
While there is nothing wrong with understanding both redirective and non-redirective designs, this is where it really matters in a real decision.
A non-redirective cushion has less strict testing requirements than a redirective cushion, which is not actually heavily disturbed by an impacting vehicle, but instead is able to bounce it back into the traffic stream.
When an angled side-impact is a real possibility, such as on a busy multi-lane highway, redirective designs provide greater protection.
In cases where the only realistic scenario involves the collision with a non-redirective unit, such as on a narrower, less traveled road, it may be entirely appropriate to use a non-redirective unit.
Inquire from suppliers directly which category the unit belongs to and don’t settle for “it’s a good all-rounder” being a true answer.
Choose Sacrificial vs. Restorable Designs
The decision will depend on the frequency of contact, rather than on the frequency of catastrophic impact.
Sacrificial systems absorb the energy during a crash and are consumed then and used once; restorable systems absorb energy during a smaller impact, and then reset and get used again.
In a highway speed construction zone, any contact generally is serious, and the eggs are often sacrificed which are designed to be used once.
Units are more likely to be restored in a slower urban setting where minor accidents occur much more often than major ones, and in which a hydraulic-based unit performs better than a restorable unit.
Be honest here; consider what your actual traffic situation is, and not take the high priced one as the smart choice.
Ensure That the Host Vehicle Is Capable of Supporting It on TMA crash cushion
This is the most hazardous omission on this list, and it’s done a lot too rarely.
A TMA’s crash rating is only as good as the truck it is being installed on and the ability of the truck to anchor the TMA in the event of a crash.
TL-3 rated systems generally demand a minimum 26,000 lb gross vehicle weight rating (GVWR) host truck, and installing a correctly rated cushion on an undersized truck defeats the whole purpose of the engineering.
When making your final decision, make sure that you verify the specific GVWR the unit will be on, not simply the rated GVWR for the cushion by itself.
Verify Your Certification the Right Way, NOT the Easy Way!
After you’ve narrowed down the type, rating and host vehicle, the next filter is certification – not something that should be skimped on, but done correctly.
Request the unit’s documentation based on a specific serial number that the unit has conformed to a tested configuration per the MASH or NCHRP 350 standards instead of a generic statement of being certified as a model line.
If it’s not brand new, confirm when that unit was last recertified.
The first thing that should be noted is that a unit that has been in a yard for several years, and exposed to the intense UAE sun, is more worthy of a careful inspection than a newly made unit.
Consider the Pros and Cons of Renting vs Owning Honestly
At this stage you should know the rating, type and certification that you need.
The final question is whether or not you will rent it, or buy it, and this, of course, depends on how often you use it.
If your project list is continuous, year round, it may be financially viable to own.
With work contracts staggered with periods of downtime between them, it makes more sense to opt for rental, as you are not binding up capital in equipment that is not being used for part of the year.
Whatever it is, the crash rating and the crash testing standards used should be the same as they wouldn’t want to rent the less-tested unit.
Five-Question Checklist Before You Commit
Check those prior to signing any documents:
- What is the actual speed of the road, not the posted speed?
- Is it a static or moving work?
- Is the cushion type appropriate for realistic impact angle of that road?
- Does the host vehicle have an adequate weight rating for the cushion’s TL classification?
- Can the supplier provide serial number specific certification documentation when requested?
If you can give a clear answer to all five, you aren’t basing your choice on guesswork or a pretty product page, you are making an engineering decision.
Why a Rush Decision Is Wrong
This is an easy process to think of as a formality and just grab what is easiest to come by.
It’s a natural instinct when there’s a deadline, but it reverses the risk.
A mismatched unit, a wrong rating on the speed, a wrong type on the impact angle and undersized host truck don’t fail loudly in a quote or brochure.
It doesn’t fail with a lot of noise until it is really tested by a real collision.
The Bottom Line on How to choose the right TMA crash cushion
When it comes to picking the right TMA crash cushion in the UAE, it is actually all about the logical process that you put together as opposed to comparing the price tags.
Test with real road speed, choose between static or mobile deployment, choose the cushion redirective and absorption type based on realistic impact scenarios, ensure the host vehicle is capable of certifying down to the serial number, and ensure the cushion is in good operating condition.
Then, the unit you get isn’t the one that’s pretty on paper.
It’s the one that’s really designed to do the thing you’re going to do.