What If Roads Lasted Twice As Long?
Texas has 311,000 miles of road, more than any other state and nearly twice the total of the runner-up, California. The state spends $10 billion per year on transportation, and the Texas Department of Transportation says that figure falls $5 billion short of the investment that's needed, largely to pay for road maintenance.
If there were a better way to take care of roads in the Lone Star State, it would be a very valuable idea.
Enter Sahadat Hossain, an associate professor of civil engineering at the University of Texas at Arlington and the man behind a new state program to shore up crumbling roads using an underground support system of recycled plastic pins.
"Just think about it," Hossain says. "You need one million dollars to repair something. Or you can use a sustainable recycling material and do it for $200- or $300,000. You don't need to be an engineer to see that."
The scheme's low price is matched by its high effectiveness. In a two-year feasibility study that concluded this August, sections of Texas Route 287 with 10-foot-long pins drilled into the roadway slope moved only one to two inches. The control sections, left unsupported, moved 15 to 16 inches.
Much of Texas is built on what's called "expansive clay," a type of soil that swells and contracts with unusual vigor during wet and dry weather. The result is that roads there buckle and crack much more often than in the Northeast, Midwest or Mountain West, where the ground is more firm.
Courtesy USGS. From most volatile "expansive clay" to least: red, blue, green, brown.
On elevated roads, particularly sections leading to bridges, embankments quickly begin to slip. Highway engineers call this "slope erosion," and many such roads require serious repairs every five to ten years. With reinforcement, Hossain predicts highways will last 15 to 20 years before needing maintenance.
The input cost of the pins, which have previously been tested in Missouri, is less than 50 percent that of traditional highway support measures like retaining walls. And because they are made from recycled plastic—each pin contains about 500 soda bottles—the pin concept turns plastic's non-decomposition from an environmental headache to an engineering solution.
Workers insert plastic pins underneath Texas Route 287 as part of a pilot program that concluded this summer. (Courtesy Sahadat Hossain/UTA/TxDOT)
With a million-dollar grant from the state DOT, Hossain is now beginning to implement the plastic pin solution on two other Texas Highways, Routes 183 and 360.
While each soil type requires new research into pin design and placement, Hossain thinks the program could easily spread to other states and beyond.
"Eventually, the idea is going to catch on internationally," he says. "I'm confident."