Attenuators

ADOT explains: What’s an attenuator?

ADOT explains: What’s an attenuator?

ADOT explains: What’s an attenuator?

ADOT explains: What’s an attenuator?

By David Woodfill / ADOT Communications
November 28, 2023
A traffic attenuator after a crash.

You likely have no idea what the contraption in the above photo is called, even though you probably drive past them every day.

They're called crash attenuators and they’re simple, efficient and safe devices that can absorb the impact of a vehicle collision, while protecting the lives inside.

We have several kinds of attenuators – fixed attenuators, truck-mounted attenuators and crash barrels are common types – to choose from, depending on the situation and need.

Here, we're going in-depth on fixed attenuators, more specifically, "Smart Cushion Impact" attenuators. Smart Cushion Impact attenuators utilize a clever combination of hydraulic pistons and pulleys, and they ingeniously collapse in on themselves, taking the full brunt of a vehicle driving at highway speeds while working to safeguard vehicle occupants.

Another feature is that Smart Cushion Impact attenuators can be reset and used over and over again. After a crash, when all those involved have been tended to, any law enforcement investigation has been completed and crash debris removed, ADOT workers swing into action and a heavy-duty work truck and chains to pull the attenuator back into its position.

This process is remarkably swift, clocking in at about 30 minutes. Other fixed attenuators, which use a combination of concrete and foam, need to be reconstructed and that demands considerably more time.

So, next time you're driving on a highway, take a moment to appreciate these ingenious devices. Better yet, exercise attentive, safe driving habits so that you never have to experience one up close.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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All about attenuators

All about attenuators

All about attenuators

All about attenuators

May 27, 2014

From top: An example of a fixed attenuator that has been hit. Truck-mounted attenuators. Sand barrel crash cushions.

Attenuators are important features that help keep drivers and ADOT crews safe.

They’re also something we’ve blogged about before, but since it’s been a couple of years, we thought we’d revisit the topic for our newer readers…

First, let’s talk about the types of attenuators you likely see every day during your commute.

These fixed attenuators are placed at the end of barrier walls on the freeway. You’ll see them near off-ramps or medians and anywhere a barrier wall comes to an end.

They are designed to take the impact of a vehicle collision and absorb a lot of the energy from a crash.

As we said back in 2011, this is by no means a physics blog, but a basic grasp of how energy works is needed to understand attenuators.

A vehicle’s speed and size determine how much energy it has. Normally, this energy is dissipated by your brakes, which burn off that energy slowly, allowing you to come to a safe stop.

But, if a vehicle stops by crashing into a wall, the energy is dispersed very suddenly, resulting in a car that’s crushed. Attenuators won't exactly give a soft landing, but they do work to dissipate the energy slowly like your brakes do. Various attenuators do this by different methods.

Next up, is the truck-mounted attenuator. You might have seen these, too, during your commute.

They’re the big rectangle-shaped “boxes” attached to the back of certain ADOT trucks. Inside that attenuator “box” is just a honeycomb configuration of aluminum, Styrofoam and air space.

They're simple, but they save lives and act as a kind of shield that stands between freeway traffic and ADOT crews. If a motorist travels into a freeway work site they’ll hit the attenuator instead of a heavy truck, or ADOT workers.

The truck-mounted attenuator, like the fixed attenuator, is designed to take the impact and crumples together as it absorbs the energy of the vehicle.

Now, let’s look at ADOT’s use of sand barrel crash cushions.

Like their name implies, sand barrel crash cushions are filled with sand, shaped like a barrel and work to provide a “cushion” if a vehicle were to crash into one.

A sand barrel crash cushion works similarly to the way an attenuator functions.

You’ve probably seen them several times on the side of the road. They’re placed strategically in front of fixed objects (signs, poles, etc.) and will take the impact if a driver runs into them.

They can be set up in different configurations depending on speed limits and the specifics of the location.

One common setup consists of 12 barrels (although, there are numerous variations). You’ll often see four of the barrels lined up single file. Behind those first four, there typically will be four more rows with barrels lined up two by two.

The weight of each barrel varies – they weigh 200, 400, 700 or 1,400 lbs. The lightest barrels are placed in front and they get progressively heavier to handle the impact, absorb and dissipate the energy of a crash.

Vehicles of ADOT: Bucket Trucks

Vehicles of ADOT: Bucket Trucks

Vehicles of ADOT: Bucket Trucks

Vehicles of ADOT: Bucket Trucks

December 5, 2013

This bucket truck extends up to 45 feet.

With more than 6,000 miles of highway to oversee and maintain, ADOT relies on its fleet of trusty vehicles to help get the job done. We’re not referring to your everyday trucks and sedans – we are talking about heavy-duty equipment, designed and built to perform some enormous tasks.

Because these vehicles play such an integral role in ADOT’s everyday operations, we thought it’d be fitting to highlight some of them here on the blog.

So, let’s get things started by introducing you to ADOT’s bucket trucks…

Extending up to 45 feet, these trucks are used primarily by ADOT’s Signal and Lighting crews to repair and maintain traffic signals and lights.

The bucket truck is used to repair traffic signals, freeway lights (the shorter poles) and the lights that shine underneath bridge decks.

2013-1205-bucket_truck

The bucket trucks have compartments used for supplies.

By the way, there is also a larger bucket truck available that’s used to work on the taller freeway light poles – it reaches 68 feet.

Before an ADOT crew member can get in the bucket and head on up, they have to stay safe and put on a full-body harness and a hard hat. Also, before the bucket will elevate, a couple of stabilizers extend out of the sides of the truck (kind of like hydraulic kick stands) to keep things nice and steady.

Another safety factor – two crew members go out with these trucks. One person operates an arrow board/attenuator truck (to warn traffic) and one will be up in the bucket making repairs to the light or signal.

One more thing about these trucks is that they have several compartments that allow crews to carry along all the supplies necessary to make a repair.

You can learn more about ADOT’s Signals and Lighting crews, by reading some of our previous posts. And, be sure to stay tuned for upcoming blog posts about the Vehicles of ADOT.

Safety is top priority for ADOT maintenance crews

Safety is top priority for ADOT maintenance crews

Safety is top priority for ADOT maintenance crews

Safety is top priority for ADOT maintenance crews

October 8, 2013

We’re big fans of ADOT’s maintenance crews and we appreciate all they do to keep the roads safe…

We try to document much of what their jobs entail here on the blog, but these crews are responsible for so much that it’s difficult to capture it all (we have tried, though. Read our previous posts on the maintenance team).

Today’s video does a very good job of summing up what the maintenance crews do and why it should matter to the traveling public.

“Safety is priority No. 1,” says ADOT Highway Operations Supervisor Jerry Turner in the video above. “Making sure that the public has a safe road to travel on, whether we’re repairing guardrail or picking up debris on the road.”

The video also provides a reminder of how important it is to give these crews some room if you spot them working on the side of the road (remember Move Over AZ?).

“They are working to make your world safer. Give these folks a break,” says Public Information Officer Doug Nintzel. “That means merging over a lane or making sure you’re slowing down if you see a maintenance crew at work.”

For more on ADOT’s maintenance crews, revisit the blog archives and learn about the many responsibilities of this group. And, if you want to learn more about the attenuators that were mentioned in the video, we’ve got that covered, too.

Attenuators designed to take the impact of vehicle collisions

Attenuators designed to take the impact of vehicle collisions

Attenuators designed to take the impact of vehicle collisions

Attenuators designed to take the impact of vehicle collisions

December 20, 2011

An example of a fixed attenuator
that has been hit.

Back in July we told you all about truck-mounted attenuators and how vital they are to the safety of ADOT employees and drivers out on the road. 

But, there’s another type of attenuator that acts on the same principle and does just as much to protect motorists...

Instead of being attached to a truck, fixed attenuators are placed at the end of barrier walls on the freeway. You’ll see them near off-ramps or medians and anywhere a barrier wall comes to an end.

Like truck-mounted attenuators, fixed attenuators will take the impact of a vehicle collision and absorb a lot of the energy from a crash.

This is by no means a physics blog, but a basic grasp of how energy works is needed to understand attenuators …

A vehicle’s speed and size determine how much energy it has. Normally, this energy is dissipated by your brakes, which burn off that energy slowly, allowing you to come to a safe stop.

But, if a vehicle stops by crashing into a wall, the energy is dispersed very suddenly, resulting in a car that’s crushed. Attenuators won't exactly give a soft landing, but they do work to dissipate the energy slowly like your brakes do. Various attenuators do this by different methods.

There are a few different types of fixed attenuators; however most of them will look pretty similar to drivers.

Some of the brands are built on a rail and have several compartments that hold Styrofoam blocks to absorb the impact. When a vehicle crashes into it, this type of attenuator, also known as G.R.E.A.T.s and QuadGuards, will collapse a compartment at a time and the blocks will disperse the energy. ADIEM's are made of a gypsum type composite that sit on top of an inclined base.

Another attenuator brand, known as the SCI Smart Cushion, is very similar, but instead of Styrofoam, these types of attenuators use a cable and hydraulic ram to absorb the energy.

Location and the area’s speed limit help determine which brand attenuator gets placed in certain spots.

Once an attenuator is hit by a vehicle, it needs to be fixed. ALERT Commander Tom Donithan says repairs vary depending on the type of attenuator and the severity of the crash.

Repairs to the types of attenuators designed to use Styrofoam blocks call for replacement of the blocks and other components.

Generally, the SCI Smart Cushion requires pulling the system back out and the replacement of a few bolts after it has been hit. The front shield also usually is replaced (see photo above).

Typically ADOT crews repair about five attenuators a month in the Valley region. If they’re badly damaged enough, they’ll need to be replaced and Donithan says that happens about three or four times a year in the Valley.

“They all perform the same duty, which is to protect the public from the blunt end of a barrier wall” said Donithan, adding that attenuators perform their job well and that there are very few times that his team comes across an attenuator crash where the driver doesn’t walk away.  “That’s why they’re out there, because they do their job”

Attenuators offer safety on the freeway

Attenuators offer safety on the freeway

Attenuators offer safety on the freeway

Attenuators offer safety on the freeway

July 6, 2011

Attenuators act as a barrier between traffic and ADOT crews. Check out the slide show below to see how attenuators take an impact.

Sometimes the simplest concepts work the best.

Take for example the truck-mounted attenuator. Maybe you aren’t too familiar with them, but chances are you’ve seen one when driving on the freeway.

They’re the big rectangle-shaped “boxes” attached to the back of certain ADOT trucks. And, while the attenuators may not look fancy or impressive, they save lives.

“Anytime we’re going to be working on the side of the road, we use them,” said ADOT Maintenance Superintendent/ALERT Supervisor Tom Donithan.

Inside the attenuator “box” is just a honeycomb configuration of aluminum, Styrofoam and air space, according to Donithan.

Attenuators act as a kind of shield that stands between freeway traffic and ADOT crews. If a motorist travels into a freeway work site they’ll hit the attenuator instead of a heavy truck, or ADOT workers.

While it’s likely not a soft landing, the attenuator is designed to take the impact and crumples together as it absorbs the energy of the vehicle.

“They do their job. We don’t go on the road without them,” Donithan said.

ADOT has been using the truck-mounted attenuators since 1990 and Donithan says typically at least one gets hit each year – but there have been four hit so far this year.

Truck-mounted attenuators are for the protection of drivers and the ADOT employees working on the roads. They’re so useful that Donithan says if an attenuator isn’t available, then his crews will wait until one is ready before heading out to the freeway.

“We take it very seriously because it is our lives and our co-workers lives,” he said. “If you didn’t have the attenuator there, your chances are much higher if you do take a hit, that hit is going to cost someone’s life.”

Attenuators