Iowa DOT News

Audible attenuators increase awareness of short-term work zones

AMES, Iowa – April 29, 2021 – Iowa Department of Transportation crews have shifted from plowing snow to spring and summer maintenance activities like patching potholes and painting road markings. These activities often take our people out of their trucks onto the roadway, dangerously close to speeding traffic.

To help reduce the risk to our crews and everyone else who is on the road, we employ a number of safety practices including the use of audible attenuators on short-term, stationary, or slow-moving maintenance operations. The attenuators are designed to warn drivers of crews ahead and take the impact of a crash if a driver does not slow down or move over for the crew.

An attenuator is a trailer that is pulled behind a truck equipped with flashing lights and signage signaling the presence of crews. If a driver does not appear to slow down or move over for the crew, the attenuator operator has the ability to turn on additional flashing lights that shine at a higher frequency. If a driver is still not responding to the extra lighting, the attenuator operator can then activate an audible sound in a final attempt to get the attention of the driver. 


Instances of our crews being hit are an ongoing problem. In 2020, there were five crews hit and two members of the DOT family lost their lives. So far in 2021, we’ve already had four crews hit by motorists.

Brad Fleming of our Maintenance Bureau says the number of trucks being hit is impacting the willingness of employees to drive the attenuator trucks. He said, “Our crews have a sense of duty to get the job done. They are dedicated to their work, but we have very few employees who haven’t seen or been involved in a near-miss or a crash due to an inattentive driver.” When drivers aren’t paying attention, sounding the audible attenuator is designed to be loud enough to get the attention of the driver and has the added benefit of signaling to everyone around that the crew is in imminent danger of being hit.

Fleming added “Although you may not be aware of these audible attenuators, they are very similar to fire or law enforcement sirens. We recognize the sound from the attenuator has the potential to be disruptive to those in the area. We hope that those that are hearing the sound recognize the value it brings to the safety of our crews and treat the disruption like sounds they would hear from other emergency response vehicles. Just like those sirens, these audible warnings are used to increase the safety of not only our crews but all of those who share the road Our crews don’t like the loud sound any more than others in the area. That’s why we reserve its use for when we feel it could be a life or death situation.”

The Iowa DOT currently has 39 audible attenuator systems in place and 32 more systems should be in place this year. Each system is built by Iowa DOT staff and costs approximately $10,000. While the current systems are manually triggered by an operator driving the attenuator truck, Fleming says testing will begin this spring on an automated version of the system that will be triggered when a vehicle approaches a work zone too quickly or too closely.

Keeping you safely traveling down Iowa’s highways is our main goal. Audible attenuators are just another step in what we are doing to hit this goal.


Contact: Brad Fleming at 515-239-1628 or [email protected]

Video clips:

Cell phone video shot by one of our supervisors shows a crew patching I-80 in the Des Moines area who were forced to activate the audible attenuator to not only warn inattentive drivers of the crew's presence but also warn our crews that they were in imminent danger of being hit.

Interviews with central Iowa paint crew staff:

Corey Baptist – Garage Operation Assistant and lead worker, Central Iowa paint crew

Chad Rumbaugh – Highway Technician Senior, Central Iowa paint crew

Scott Smyth II – Highway Technician Senior, Central Iowa paint crew


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