To Chip or Not To

Annual chip sealing creates headaches


The toxic scent of oil and tinkling of loose rocks hitting the underside of your car is as much a sign of summer in Boise as minivans heading for the waterpark or the drone of air conditioners.

The annual rite of chip sealing has been part of summer in the Treasure Valley for three decades. Each year, the grumblings of drivers and bikers lead us all to wonder why, exactly, road maintenance means praying your windshield doesn't end the season as pock marked as the lunar landscape.

While it may seem arcane (especially as a you try desperately to keep your bicycle from careening into oncoming traffic while riding over an uneven, bumpy surface), for officials with the Ada County Highway District, it's the best—and least expensive—way to keep the county's roads in shape.

This year alone, 244 miles of ACHD roads will be resurfaced with chip seal. While that fact may raise a communal groan, ACHD has its reasons.

The main one—cost. "It's nearly nine to 10 times cheaper than the [asphalt] overlay," said Jim Michaelson, superintendent of operations at the ACHD Cloverdale Maintenance center. "It lengthens the years you get out [of roads]. It's the cheapest maintenance thing you can do."

Chip sealing a road costs roughly $15,000 per mile. An asphalt overlay costs $200,000 per mile.

The price-per-mile cost is one reason chip sealing is used across the country, although the hot, dry summers in the West make it more common in this region because those conditions are required for the process.

Other Western cities like Portland, Ore., and Denver use chip sealing, and several cities in California that had stopped the practice have returned after they were unable to afford to maintain roads with other methods.

Most drivers still aren't convinced that it's the best option. According to the Insurance Information Institute, drivers spent an estimated $2.4 billion nationally for windshield repair and replacement in 1997. That number has been steadily on the rise since auto makers have used increasingly lighter glass to help fuel efficiency, and the amount of road construction has continued to grow.

In Ada County, the number of roads ACHD maintains has grown with the valley's population—459 miles of new roads since 1998. Michaelson's region, one of two in Boise, has grown from 86 miles in 1998 to 132 miles. Currently, there are 2,110 miles of roads in the county.

While ACHD takes a zone approach, breaking the county into 18 territories, two of which are resurfaced every nine years, more roads mean a longer chip-sealing season. In the past, chip sealing began the week after July 4 and ran through the beginning of September. This year, crews began work June 4 and will continue through mid-September, Michaelson said.

Michaelson said he's well-versed in driver complaints, but both complaints and insurance claims have dropped since ACHD began using new techniques and smaller rock pieces.

"The biggest thing is to stay on top of the curve," he said. "We keep using it and keep people as happy as we can. Most people accept it—bikes don't like it, but you've got to take care of your roads."

Three years ago, ACHD began using a latex-modified oil as the sticky portion of the chip-sealing recipe. Michaelson said this mixture sets more quickly than oil used in the past, helping cut down on the amount of loose rocks.

The agency also decreased the size of rock chips in its mixture, going from one-half inch to three-eighths inch in diameter, creating a smoother road surface. ACHD has also experimented with using one-quarter-inch chips along heavily traveled bike paths, including the Hill Road corridor.

While road bikers still don't particularly like chip sealing, they do like the new bike lanes.

Bicyclist George C. Knight said the improvements are both noticeable and appreciated, but he's still not a huge fan of chip sealing. "It's treacherous to ride on when there's fresh chips," he said. "We share a dislike for the ongoing construction projects [with drivers]. More and more, as we continue building in the valley, it's harder and harder to find a route that avoids construction sites."

Knight has carefully watched developments on area roads for years and recently joined ACHD's bike advisory committee to advocate for the needs of bikers. He said chip sealing is a perennial issue, especially as more people move to the valley.

"It's astonishing to them," he said of new residents moving from areas without chip sealing. "Personally, I wish I didn't have to ride on those surfaces. It helps maintain debris, and it's hard to clean, even after a sweeper. There's broken glass and metal shards—I don't want to ride over that stuff any more than I want to ride over chips," he said.

Ada County is the only county in the Treasure Valley using the smaller chips. Both Canyon and Gem counties still use one-half-inch chips. "The chips (rocks, gravel, boulders) that are used in Gem and Canyon county are horrible," said David Bartle, coach of the Boise Young Riders Development Squad and head of the advisory committee in an e-mail statement.

Michaelson said ACHD tries to minimize the chance for damage during the chip-sealing process. It all starts the year prior, when crews repair concrete and asphalt, and deal with curb damage and drainage issues. Crews then apply a scrub coat, a thin overlay applied before chip sealing.

When the main project begins, an oil truck sprays the latex-modified emollient (made of equal parts oil, water and latex). The oil is quickly followed by a truck that spreads the pre-sized rock chips over the surface. Michaelson said new technology allows for better control over the amount of chips dropped, so there is less loose gravel. The new equipment has decreased the amount deposited from 25 pounds per square yard to 16 pounds per square yard.

"It's just enough to cover the oil, but it helps with chips," he said.

The chipper truck is followed by large rollers, which force the loose chips into the oil. The mixture takes roughly 20 to 25 minutes to set, but it could take months to fully cure, Michaelson said.

Depending on how busy a street is, a street sweeper cleans up the loose gravel between one day and one week later. Finally, an oil and water mixture called a fog seal—to further lock down the rock chips and give the road a black color—is applied a week later.

"People tend to like the black better than gray," Michaelson said.

While chip sealing is used widely across the valley, it's not the only technique ACHD uses. Concrete is the medium of choice on some of the area's largest intersections, including at Overland and Cole roads and State Street and Veterans Memorial Parkway.

Concrete is more expensive than asphalt to install, but it lasts far longer. Michaelson said ACHD is considering using concrete at other major intersections to cut down on maintenance.

But even with these intersections, it's a safe bet chip sealing will continue on Ada County roads. So, what can you do to minimize the possibility of getting your windshield taken out by a flying rock chip? Michaelson said slow down.

"If citizens would drive at speeds we put out there for rock chipping, no one would get a rock chip," he said, adding that few people actually drive the posted 20 m.p.h. speed limits.