Drivers sarcastically call it the New Mexico state tree, but really, the ubiquitous orange highway barrel is more of an invasive species.

Every year, groves of them appear all over the state, disrupting native traffic flow and stressing commuters as they head off to work.

A project at The University of New Mexico, however, could one day significantly reduce the number of orange-barrel outbreaks across the state — by creating roadways that last longer and need repairs less frequently than normal ones.

Right now it's just a research project, but Rafiqul Tarefder, a professor in the School of Engineering, is working on designs for perpetual pavement, which is a type of pavement designed to last 50 years or more, he said.

"Perpetual, it means forever, but in the pavement business, nothing really lasts forever," Tarefder said.

Normal asphalt pavement in New Mexico is designed to last about 20 years, but it needs periodic maintenance to keep it sturdy. After about 15 years, workers have to mill and inlay the top layer to restore the structure, said Bob Meyers, geotechnical selection manager for the New Mexico Department of Transportation.

"Eventually no matter what you do to the surface of that, though, the bottom mat of the pavement has to be replaced," Meyers said. "That's because the bottom mat cracks, and when it reaches that point, no matter what you do to the surface, you're just wasting money."

Pavement is generally made up of three layers, each of varying thickness. The mat, or base, is the lowest and most permanent level. The intermediate layer is sort of a buffer section. And the surface layer is the least permanent and most subject to wear by traffic.

"So what we're looking at is the kinds of layers, the strength of different materials in them and the thickness," Tarefder said. "We have tools that can tell us when you apply a bed of pavement, how much cracking, deformation or strain you can expect."

The goal is to make a lower and intermediate layer that don't need to be replaced for at least 50 years, and possibly much longer, and also to make a top layer that's more durable, he said.

"If you think about asphalt, it's like a glue, we mix rock and aggregates together with binders or polymers," Tarefder said. "What some of my students are looking at is what happens if we put in things like carbon nanotubes, some anti-stripping additives, or even things like lime."

Tarefder, his students and other researchers at the university have been working on the perpetual pavement project with DOT for about a year now. So far, they've tested thousands of pavement types.

They've finished one type of perpetual pavement already, designed for roads that carry up to 1,750 annual average daily truck traffic, or AADTT, which is a unit of measurement used by road designers.

U.S. 550 and U.S. 70 are both roads that have loads similar to that level.

"You can say that's moderate traffic, and we've finished that," Tarefder said. "The next step is to figure out high traffic."

Both I-25 and I-40 have larger AADTT loads that will require much stronger permanent pavement, he said.

I-25 has an AADTT of between 3,000 and 5,000, and I-40 has an AADTT of between 5,000 and 10,000.

Tarefder said he expects to have found a type of permanent pavement good for those roads by sometime next year.

Tweaking the thickness of levels and making them more durable can significantly cut down on the amount of maintenance a road will need, but finding the right balance is also critical, and can save a lot of money, Tarefder said.

"If you overdesign an asphalt layer by one inch, we're talking between $500,000 to $1 million per lane mile difference in the cost," Tarefder said. "If you go 20 miles, the state is spending an extra $10 million to $20 million in that scenario."

But while New Mexico drivers will certainly be happy with the notion of less construction, and while the research at UNM looks promising, there's still no guarantee that the project will ever come to a point where the rubber actually meets the road, Meyers said.

When asked how many roads were set to use the new pavement type, Meyers answered quickly.

"None," Meyers said. "It's a research project."

The problem with using the technology is that it costs a lot more upfront, although generally permanent pavement pays for itself and even saves money in the long run.

"It's a different policy for looking at public money," Meyers said. "It involves more long-term thinking."

Up front, permanent pavement can cost two to three times as much as a 20-year pavement. But beyond the maintenance costs saved over the years, it also has some harder to define benefits, such as economic productivity that's increased when workers don't face as many traffic construction delays, he said.

"There's also the cost of detours, temporary travel lanes and things like that," Meyers said. "After 50 years you're going to be spending less."

Another problem with permanent pavement, however, is that some designs that were developed in other states have proven to not be as durable as advertised, Meyers said.

"Some other states that have used this have had some problems," Meyers said. "There have been some cracking and permeability issues."

Still, UNM's goal is to get around those problems, and make something that will last and will save money over the traditional 20-year designs, Tarefder said.

"We think these designs are very attractive," Tarefder said. "And we hope that we can work together and come up with something that doesn't disrupt traffic as much and is cost effective."

Contact Sue Vorenberg at svorenberg@sfnewmexican.com.