How do we know what roads to fix when?

TAMlogoRoads and bridges don’t last forever. At the Iowa Department of Transportation, we need to keep a constant watch on the condition of our transportation assets. That’s where transportation asset management comes in. This is the third post in a series of articles about how the Iowa DOT evaluates and manages Iowa’s transportation system using a transportation asset management plan. 

In general, transportation asset management is all about providing the right treatment to the right asset at the right time. The Iowa DOT considers an asset to be any of the more than 9,400 miles of road or nearly 4,200 bridges on the state system, roads marked as state highways, U.S. highways, or interstates. County road and city streets are not part of the state system.

For this blog post, we are going to focus on “pavements.” We use “pavement” instead of “road” when we discuss condition of the driving surface, whether it is made up of asphalt or concrete. We’ll take up the topic of bridges in the next post. 

How long can we expect a pavement to last?

The majority of roads on the state system were constructed from the 1920 to the 1960s. In the past, asphalt pavements have been designed to last 20 years and concrete pavement 40 years. By doing a little math, you’ll see many of our highways have long exceeded their expected useful life. But life expectancy numbers don’t tell the whole story. The Iowa DOT is shifting its philosophy on pavement lifecycles away from a prescribed number of years and moving toward using performance criteria to define the end of a pavement’s useful life. 

This chart shows the original construction date of our pavements and the number of times they have been overlayed.

What methods are used to determine pavement condition?

We use two methods to look at how a stretch of pavement is holding up, visual inspection using computer-analyzed video and instrument or machine testing. The data gathered from these two methods is analyzed to determine the condition of the pavement and the need for pavement rehabilitation.

For the visual inspection, the Iowa DOT hires a company to drive every state-maintained highway each year. The vehicle used has specialized equipment that captures video of aspects of the pavement. The video is computer-analyzed and reports are generated about the condition the pavement is in. Visual inspection is a good way to identify cracking or other signs of pavement wear.   

Scott Schram, of the Office of Construction and Materials, said, “There are different types and severities of cracks. A serious crack or other pavement issue found by visual means can be a symptom of a bigger problem. By analyzing the amount and severity of the cracking, we can begin to get a picture of why the cracks are happening. It’s a lot like when you have a fever and go to the doctor. You want the doctor to find the cause of your fever. We act as the doctor in this case and explore the cause of the crack.” 

SmoothnessmapWhile the visual analysis is a good way to find cracks and other fairly obvious issues, the Iowa DOT tests for other elements of pavement condition using instruments or machines. “Smoothness is probably the thing motorists notice the most,” said Schram. “But we also check for friction, or how much your tires stick to the pavement; rutting, where your tires wear a groove in the pavement; and pavement structure, whether the pavement is sufficient to carry the amount and weight of traffic that rumbles over it every day.” 

Friction skid resistance
This trailer tests for friction and skid resistance.

Each year all Iowa DOT-maintained highways are tested for smoothness and rutting. Schram said, “For friction and structure testing, we have a cycle that runs about every five years for areas where no issues have been identified. For areas where the pavement has shown some cracking or other structural issue, we test more frequently.” 

The results of all these tests are brought together into what is known as the Pavement Condition Index (PCI). Matt Haubrich, Iowa DOT asset manager, said, “The PCI is used to help us look at the big picture to see how the transportation system is performing and whether we’re investing  in the right areas to keep the system sustainable. This is a balancing act. We have limited funds and we need to make sure we are making the best investments now to maintain the transportation system for the future.” 

Scott-pull-quote“The benefit of having all this data goes beyond knowing how our pavements are holding up now,” said Schram. “We have the ability to use data, when combined with traffic information, to predict how the pavement will stand up over time.
This helps us plan for future needs much more effectively. Using the data from our investigations, we run software programs that lay out thousands of different scenarios on how to best spend the dollars we have. Using that software, we can predict with a high level of accuracy what projects will have the biggest impact for the cost.”

Different conditions require different treatments (or combinations of treatments).

So, going back to the medical analogy Schram used, a doctor doesn’t use the same medicine to treat all ailments. The Iowa DOT doesn’t use the same treatment on every road. The data will help us determine which roads need surface repairs and which ones need much more extensive rehabilitation.

As you may remember from the last blog post, doing this analysis doesn’t always mean that the roads in the worst shape will get a treatment first. Sometimes we’ll choose to invest in a pavement or bridge before it deteriorates into poor condition and require a much more expensive fix.

Here’s another way to look at transportation asset management. Think of the roof on your house. If some shingles blow off or are damaged, it is relatively cheap and easy to replace them with a few new ones. But if those same damages shingles are not replaced or repaired, it won’t take long for a leak to develop and then you have a big problem with damage beyond what is on the surface. Waiting often adds up to a much bigger bill. It’s the same with our roads. Sometimes the money is best spent on several smaller repairs to prevent larger repairs in the future.

That’s not to say the larger repairs aren’t happening, it’s just that we’re being very strategic with the limited funds we have to keep the system running. 

What’s next?

Over the several months, we will continue to follow the progress of the transportation asset management planning process and tell you more about key elements of asset management, including answering questions like: 

  • How do we plan for the needs of bridges?
  • How do we plan for future maintenance needs?
  • How do we put a price on our assets?
  • Where does the money come from?
  • How do we determine how much to spend and on what to spend it?

If you missed the first two articles on TAM, you can read them here:


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