Listen With little money devoted to roads, experts say pothole season could be worst yet
Mar 13, 2011
The war on potholes in Minnesota includes a search for ways to prevent them. Road experts say they're making progress on that front, but many of the ideas are expensive and in the meantime, the worst of the pothole season is still to come.
Don't blame the pothole crews. Weather permitting; they are out on Minnesota's roadways diligently shoveling and tamping asphalt mix into potholes.
The long search for pothole fixes, MnDOT engineer Tim Clyne said, includes finding a better asphalt recipe. Clyne leads a staff of eleven at the Minnesota Department of Transportation's pavement test facility.
The facility is a stretch of freeway north of the Twin Cities, where Clyne and other engineers tease the very highest performance from asphalt, a mix of what's called asphalt cement and aggregate, to make the state's most widely used road surface.
"We can do a lot of things with the asphalt binder, the black glue, the sticky stuff that holds the rocks together, and basically by using a softer asphalt binder it's able to withstand those stresses, it can stretch a lot further before it actually cracks," Clyne said.
That helps on the front end when building a road. But as time passes and cracks form, asphalt succumbs to the weather — hot and cold, freezing and thawing — along with the onslaught of traffic. Filling the holes is a cosmetic and temporary fix at best.
University of Minnesota civil engineering professor David Levinson has a long-term suggestion for addressing the pothole problem.
"We haven't invented anything that will eliminate potholes, but we can certainly reduce their number if we build roads better," Levinson said.
Levinson said, for example, it would cost nearly 25 percent more to build stronger county highways. But with money in short supply, it's an unlikely alternative.
One way to raise more money is to ask roadway users, especially owners of heavy trucks, to pay more. The big rigs already pay a lot of roadway use taxes and are only a small percent of overall traffic volume.
But Levinson and other road experts say research shows they do a disproportionate amount of damage to the roads.
"An eighteen wheeler can do 1,600 times as much damage to [the] road as a single passenger car would do over the same stretch," Levinson said.
Putting more axles and tires on the biggest trucks, Levinson said, would spread out their weight, but would be expensive and would use more energy because of increased friction.
Levinson said another partial fix for preventing pothole formation would have snow plows raise their blades an inch or so.
"When the plows touch the pavement and the pavement is cracked or uneven they often pull up chunks of pavement leading to an additional source of pothole," he said.
The problem with this idea, Levinson said, is Minnesota drivers like snow free roads so they can drive faster, rather than roads with an inch of snow on top forcing them to slow down.
In the meantime, civil engineer Dave Sonnenberg said the arrival of warmer weather portends what he calls a dandy collection of potholes.
"We're going to have a much worse pothole season then we've had in the past," Sonnenberg said.
Sonnenberg, a former Minneapolis public works director, is now in the private sector where he advises cities and counties on roadway issues.
Sonnenberg said one reason this season will be a bad one is because of more water than is usual. The ground below the roads is saturated with moisture and the area around them is covered with snow.
"We're going to melt during the day and freeze at night and that moisture is going to soak into the sub grade and it's going to freeze," Sonnenberg said. "It's going to cause that pavement to heave up; crack it even more."
Sonnenberg said another reason for the profusion of potholes is our aging Minnesota road system. He said the state has scrimped on caring for its 134,000-mile network, the fifth largest in the country.
"We've done just a very thorough job of neglecting our pavement for the last 25 years," he said.
Sonnenberg and other road experts say Minnesota is billions of dollars behind on maintenance and preservation that would slow the pothole epidemic.
But there's no state or federal plan at the moment to address our aging roadway infrastructure or to prevent the pothole problem.