If There's a Road, There's a Pothole in It
Rites of spring include the fragrance of hot tar
White chalk lines, stark against black asphalt pavement, tell a story of assault.
The lines highlight fractures like those that might appear on roads where buses or large trucks often stop with punishing abruptness.
When exposed to the elements, these small fractures could become tomorrow's gaping potholes, according to Robert Eaton, the director of the Frost Effects Research Facility at the US Army Corps of Engineers' Cold Regions Research and Engineering Laboratory in Hanover, N.H.
Mr. Eaton and his colleagues specialize in giving pavement a hard time. The test section bearing the chalk marks is a sample of his group's handiwork. It lies beneath a $20-million mobile traffic simulator that can add 20-years' wear to a patch of pavement in three to four months with a single tire. The researchers test highway materials, construction, and repair methods in hopes of giving drivers safer roads while helping public-works departments stretch their budgets.
"Road repair is the first part of the budget to get cut" when times are tight, Eaton notes. Yet the traffic on those roads continues to grow, as does the size of vehicles plying the streets. "You've got these tractor-trailer trucks carrying food to the local MacDonald's" on suburban streets designed for tamer traffic, he says.
Each year, the United States spends some $84 billion fixing streets and highways, according to John MacDonald of the American Public Works Association, based in Kansas City, Mo. But only about 40 percent of that money is spent by local governments, which are responsible for 74 percent of the nation's 2.7 million miles of highways.
State and federal spending accounts for the remaining 60 percent of the total, on 26 percent of the paved roadways. "Local governments have to do more with less," Mr. MacDonald says.
When the maintenance problem becomes acute, it often shows up as potholes. The causes are simple: heavy loads and water. In warm climates, poor drainage alongside a road or standing puddles slowly draining into hairline cracks in the pavement can lead to mushy soil underneath. Under the weight of passing vehicles, the weak spot eventually cracks, buckles, and a pothole is born. In northern climates, repeated freezing and thawing in the fall and spring can accelerate the process.
All too often, road crews take what Eaton calls the "air mail" approach to patching. "Someone stands on the back of a pickup filled with cold asphalt, heaves a few shovelsfull into the hole, then the crew drives to the next one," he says.
"We saw a pothole on Park Street near here and set up a video camera. A crew came by at 8 a.m., shoveled cold-mix into the hole, and moved on. By 8:30 the hole was empty. The crew came back three hours later and filled it again. A half hour later it was empty. Three hours later they came back. I keep hearing: We don't have time to do a more thorough patch. Yet they have the time to keep coming back to fix it."
At the same time, the role of the humble pothole patch is changing. "In the past, pothole patches were regarded as temporary fixes," says Neil Hawks, with the Transportation Research Board, part of the National Academy of Science and National Academy of Engineering in Washington. "But with 2 million miles of paved road to care for, people are coming to realize that patches must serve for long periods of time."
Manufacturers have come up with a variety of exotic materials designed to provide fast, durable patches. Though fairly expensive, they have their uses, specialists say. But, they add, effective repairs may lie less in fancy materials and more in technique.
David Reynaud, of the Civil Engineering Research Foundation in Washington, recalls a recent experiment his organization ran to test a new patching material a company hoped to sell to state departments of transportation.
Each participating public-works department picked two adjacent potholes. Crews patched one pothole using the new material. They patched the second with material they usually used. They were required to use the textbook approach to preparing and completing the patches.
When properly applied, the traditional materials appeared to yield a patch as durable as those using the new material. "The manufacturer wasn't too pleased with the results," Mr. Reynaud concedes.
Educating road crews to take the time to patch potholes properly the first time is key, Eaton agrees. "These guys want to do a good job," he says. "It's just that 90 percent of the time, they don't know any better."
Opportunities for getting it right the first time are rife. Although the federal government is spending millions of dollars on research to improve the long-term durability of streets and highways, "there is no magic bubble gum yet that you can drive on in the summertime, when it's 100 degrees out, and in the winter when it's 20 below," Eaton says. "Pavements will always crack."
And where cracks lie unsealed, potholes are sure to follow.