Iowa’s transportation network is facing two fast‑growing challenges: dangerous and unrestrained speeding in active work zones and the increasing strain of “superloads” on rural and urban roadways. Both issues carry real and lasting consequences. Speeding vehicles are one of the single biggest threats to worker and traveler safety in construction zones. Modern agricultural implements and industrial equipment superloads can weigh as much as 10,000 passenger cars causing millions of dollars in pavement damage.
Knowing that these two transportation problems have not been solved effectively with traditional approaches, Iowa DOT turned to research and data‑driven solutions to build a smarter and more sustainable path forward.
The research efforts – one which was a collaboration between Iowa DOT, Iowa State University and Iowa counties and one completed in partnership with multiple states to tackle these exact challenges – will be honored nationally with High Value Research awards from the American Association of State Highway and Transportation Officials (AASHTO) Research Advisory Committee later this summer.
Analysis shapes development of innovative superload measurement tool
In the first project, Iowa DOT focused on the growing challenge that oversized, overweight vehicles – known as superloads – pose to Iowa’s road network. While modern agricultural and industrial equipment can weigh the equivalent of 20 to 22 million tons (40-45 million pounds), existing permitting fees cover only a small portion of the resulting damage.
Because superloads vary widely in weight, axle configurations, tire types, and operating conditions, counties have struggled to accurately estimate their true impact on pavement deterioration and the associated repair costs. Iowa’s county engineers identified the need for a systematic, data‑driven method to quantify these impacts and guide more informed decisions about permitting, maintenance, and long‑term infrastructure management.
To meet this need, the Iowa Highway Research Board (IHRB) initiated a research project to develop a tool practitioners can use. Researchers – with guidance from Iowa DOT and county engineers – analyzed a large sample of Iowa roads including approximately 33,000 concrete, 25,000 asphalt, and 3,300 granular segments using 34 different agricultural and industrial superload configurations.
They assessed key damage evidence such as fatigue cracking in concrete and asphalt pavements and rutting in unpaved roads. Researchers then developed artificial neural network models to predict pavement responses for each road‑type and superload combination. Field data from real Iowa road systems validated the models by measuring stresses, strains, and deflections before and after superloads passed, and remote-sensing monitoring reinforced confidence in their reliability.
The results led to the creation of a cutting-edge modeling tool that quantifies how superloads impact Iowa’s pavements. The Road Infrastructure Superload Analysis Tool (RISAT), is a user-friendly spreadsheet tool that empowers agencies to estimate pavement damage and use that data to help protect roadway investments.
Some Iowa counties are already using RISAT to better understand superload impacts, set appropriate weight limits or permit fees, and plan sustainable maintenance strategies. The tool equips transportation agencies with a more accurate, data-backed framework for managing the long-term effects of heavy agricultural and industrial loads on Iowa’s roads. Validated by the field data, prediction models provide highly accurate for pavement responses.
Users can input information from their roadways to generate detailed predictions of damage and cost:
- Pavement type and properties.
- Road and traffic information.
- Defined superload types and properties.
- Number, weight, and spacing of axles.
- Number, width, and pressure of tires.
“The needs of agricultural and industrial transportation equipment are constantly evolving, but with RISAT, the Iowa DOT and county engineers will have a better understanding of superload impacts on our roads,” says State Research Program Manager and IHRB Executive Secretary Vanessa Goetz. “With this new tool, we can make informed decisions on how to allocate resources and create sustainable strategies for maintaining the state’s road network,” Goetz added.
Strategic speed technology deployment to slow traffic in work zones
The second project focused on the work of a nine-state partnership led by Iowa, known as the Smart Work Zone Deployment Initiative, to address the major safety concern of vehicles exceeding the speed limit through highway work zones. Iowa DOT statistics show that from 2016-2026 there were:
- 6,801 work zone crashes.
- Speeding was a factor in more than 3,000 crashes.
- Crashes resulted in 234 serious injuries and 73 deaths.
A speed reduction method that’s been widely used in the transportation industry is speed feedback trailers. These electronicmobile signs feature a digital readout of a driver’s current speed and are thought to have a positive impact as they typically trigger a self-correction when drivers see a display of their actual speed.
While they’re widely used, their effectiveness varies depending on their placement within a work zone. The Smart Work Zone Deployment Initiative - a collaboration of nine state DOTs – set out to evaluate these trailers more systematically to identify the best deployment strategies.
The research combined a literature review, a multi-state survey of current practices, and detailed field studies conducted primarily in Michigan. A total of 40 DOTs responded to the survey, with 78% using the devices and 19 states having policies for their deployment. Field evaluations showed:
- Speed feedback trailers consistently reduce speeds.
- Placement of the trailers within the work zone matters.
- The largest average speed reduction – 3.6 mph – occurred when positioned closest to active work areas.
- Additional speed reductions happened when speed feedback trailers were paired with law enforcement vehicles (1.4 mph) or digital speed limit signs (1.8 mph).
- Speed reduction effects extended at least one-half mile beyond each device, suggesting that spacing them about two miles apart is most effective when multiple units are used.
“Each year in Iowa, the DOT manages hundreds of construction and maintenance work zones across the state. Unfortunately, many drivers make decisions within these areas that put both themselves and the workers present in danger,” says Iowa DOT Work Zone Operations Engineer Brian Worrel.