Iowa testing new audible warning system on its work zone safety vehicles


The Iowa Department of Transportation (Iowa DOT) is trialling a new audible warning system on its fleet of Impact Protection Vehicles (IPVs) that act as mobile crash barriers to protect workers and equipment in highway work zones.

Also known as Truck/Trailer Mounted Attenuators (TMAs) in the USA, IPVs are always the last vehicle in the chain that is placed between workers on the road, such as a paint crew, and the flow of traffic. Its job is to warn other vehicles of the work that is being performed, as well as serve as a buffer to protect workers from oncoming traffic.

Despite already using huge orange trucks equipped with bright flashing lights to catch a driver’s attention, Iowa DOT is testing a new audible warning system that is attached to an attenuator to help increase road user’s awareness of impending work zones.

Last year nine Iowa DOT pull-behind trailer-mounted impact attenuators were hit. Fortunately, the TMAs did their job and protected the crews working ahead of them, but while safety is always the agency’s main concern, there is also a monetary cost to these crashes.

Replacement cost for each attenuator is US$14,000. If the lighted arrow board attached to the attenuator is also damaged, that adds another US$2,300 to the replacement cost. In addition to the monetary costs, the loss of use of these pieces of equipment can hold up work that the agency needs to perform and can cause delays on the state’s road network.

“Because we work so closely with other states on equipment, we’re able to share ideas and new technologies,” explained Ken Morrow, from Iowa’s Office of Maintenance. “A few years ago, we went down to Saint Louis to see an audible system they were using to protect workers on their paint crew.

“The system uses much brighter flashing lights and emits a unique sound geared toward getting drivers’ attention. It took a while to work everything out, but this summer we’re testing two systems on our paint crews in Central and Eastern Iowa and will be adding eight more systems all over the state later this summer.”

Morrow continued, “The system isn’t perfect, but it’s a step in the right direction. Currently, the audible system the Iowa DOT is using relies on the operator in the truck to activate it. In the future, we are hoping that the system can be automated so that it senses when a vehicle is approaching too quickly or getting too close.

“But for now, our operator watches traffic and turns on the system when there is a vehicle that isn’t maneuvering around the maintenance operation. For the most part, the audible sound and increased lights seem to get the distracted driver’s attention. We haven’t had any vehicles hit with the audible system in place.”

Morrow added, “The two current audible systems are being used on mainline paint crew trucks. Each system costs US$9,000. When we get the remaining 10 systems, there will be one for each of our six mainline paint crews. It will be up to district management to determine where to position the remaining audible attenuators.”

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Tom has edited Traffic Technology International (TTi) magazine and its Traffic Technology Today website since May 2014. During his time at the title, he has interviewed some of the top transportation chiefs at public agencies around the world as well as CEOs of leading multinationals and ground-breaking start-ups. Tom's earlier career saw him working on some the UK's leading consumer magazine titles. He has a law degree from the London School of Economics (LSE).