Iowa DOT using audible attenuators to increase short-term work zone awareness

April 30, 2021

Attenuators designed to warn drivers of crews ahead and take the crash impact if drivers do not slow down or move over

The Iowa Department of Transportation is employing 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. 

Iowa DOT says instances of crews being hit are an ongoing problem. In 2020, there were five crews hit and two members of the DOT lost their lives. So far in 2021, the state has already seen four crews hit by motorists.

Brad Fleming of the state's Maintenance Bureau says the number of trucks being hit is impacting the willingness of employees to drive the attenuator trucks. “Our crews have a sense of duty to get the job done," Fleming said in a statement. "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 are not 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.

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, the Iowa DOT 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.



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