Seattle street crews will spend a few days this summer getting streets in Southeast Seattle ready for another round of chip sealing, much as they did in the summer of 2003. But they'll hold off the block-by-block application of oil, chemicals and rocks until next year, according to Patricia Carroll, who, as associate civil engineering specialist for the Seattle Department of Transportation, helps manage the chip sealing program.
The work is expected to proceed June 28 through July 2, weather permitting.
"Chip sealing creates a highly skid-resistant surface," according to the city's chip sealing Web site (which was last updated to cover the 2003 program).
"It also prevents water penetration into the road's subsurface, limiting damage, such as potholes, to the street surface," the city's literature continues. "Chip sealing is cost-effective and crews can resurface up to several miles of roadway in a day's time."
Crews will apply the full treatment to another neighborhood near Haller Lake in North Seattle.
After making spot repairs, street crews will pour a special blend of polymer and liquid asphalt on selected streets, pour rocks which have been carefully sized to minimize flying into windshields, and roll the mixture down.
A small fraction of the cost of other road surfaces
The program saves the city a ton of money, according to Carroll. She said conventional asphalt paving would cost $140,800 for one mile of one 12-foot-wide lane, or $281,600 for a two-lane road-while chip sealing only costs $19,290 for one lane, or $38,580 for two. So the chip sealing saves more than $243,000 per mile of two-lane road, according to our own calculations.
(By comparison, concrete paving costs more than $2.5 million per mile of two-lane street).
Nevertheless, Carroll said the city does not use chip sealing to maintain streets that were originally paved with asphalt.
She pointed to documents that show that the city began converting dirt and gravel non-arterial streets to chip seal in 1967, in order to cut down on dust and other pollution-and improve air quality. Funding for the chip-seal work now comes from Seattle Department of Transportation's annual street maintenance budget.
Last year, SDOT crews used the chip sealing method in the Genesee Park, Seward Park and Columbia City neighborhoods. This year, crews won't be doing that kind of extensive sealing operation; but instead will work on patching up holes and evening up the streets they plan to work on.
They'll do this in neighborhoods between South Spokane Street on the north, Rainier Avenue South on the east, South Myrtle Street on the south and Interstate 5 on the west.
Carroll's boss, Charles Bookman, SDOT's manager of street paving, said this is not due to budget cuts.
"We have to finish out spot repairs first, otherwise the full chip sealing won't last," he explained. "We'll do spot repairs this year, and next year we'll be back to do the full chip sealing."
There are a few more details involved in the scenario, according to Carroll.
About one month before chip sealing begins, a crew will go through neighborhoods, with blue-on-white door hangers explaining the history and details of the chip sealing program.
The flyer crew comes from Northwest Center, a non-profit organization working throughout Washington state that employs children and adults with disabilities.
"This gives challenged people the opportunity to do things," Carroll said. "They use a map to determine the exact streets to be treated. They walk the neighborhood, mark off the streets, and mark off the catch basins [storm drains] which need to be sealed off."
Then, about a week before the actual chip sealing begins, Northwest Center sends another crew out with fluorescent orange "door hangers" advising residents that chip sealing is imminent, and not to drive faster than 10 miles per hour after the work is done.
Regular city street maintenance crews handle the rest of the jobs after that point. About 24 hours before the work starts, crews place "No Parking" barricades and signs along the sides of the streets they will seal. They also cover any storm drain inlets.
On the day of the sealing a parade of equipment lines up, including an oil spreader, gravel spreaders hooked up to dump trucks, and power-rollers, according to Carroll. And the chip sealing begins. Typical work hours are from 7 a.m. to 6 p.m. Monday through Friday with traffic restrictions in place from 7 a.m. to 3:30 pm.
"First, the tank truck sprays the hot asphalt mixture on previously surfaced roads," Carroll said.
This is not your father's (or grandfather's) "Macadam" road, she pointed out.
"Macadam used waste oil and diesel," she said. "We use a special spray which has been engineered so that we only apply a certain amount of CRS-2P polymer."
CRS-2P, it turns out, is a product manufactured by U.S. Oil & Refining Co. of Tacoma. Its formal name is "Cationic Emulsified Asphalt," according to a material safety and data sheet. It consists of asphalt, water, organic emulsifier (which suspends one liquid in another), a small amount of hydrochloric acid and a polymer. A polymer is a compound that consists of large molecules made of chemically bonded smaller molecules.
Carroll helped advise U.S. Oil & Refining to adjust the CRS-2P mixture so that people don't track tar into their homes or cars after crews spray it.
"We adjusted it so that it sticks to the pavement and dries quickly," Carroll said. "The sprayer is engineered so that it only sprays a certain amount of CRS-2P. I talked to lab specialists with the state DOT to tighten the viscosity. We want it tight enough so that it will stick, but we don't want it so tight it won't pour."
Just in case people fail to heed the "No Parking" signs, city crews actually mask cars to prevent their being sprayed with the compound (although a scofflaw resident could risk an encounter with another branch of city government, SPD, by not moving his car).
Right behind the oil truck, a rock spreader comes by, usually in tandem with a dump truck full of one-fourth-inch to three-eighth-inch rock chips. Again, Carroll said she has worked over the years to refine the size of the rock chips to make it less likely that they will knock a hole in anyone's windshield. But that's where that 10-miles-per-hour speed limit will come in.
Back to the sealing operation. Crews operating power rollers then tamp down the tar-and-rock mixture and a supervisor follows closely in a pickup truck, making sure everything is done right, and directing crews to clean up and fix any spots that need attention.
"It sets up within a few minutes and it is ready to drive on," Carroll said. "We ask people to drive at 10 miles per hour for a few weeks to allow the mixture to stabilize and to avoid kicking up rocks. It's also very slippery to drive on until it stabilizes."
Carroll said the chip sealing should last about 10 years. The city tries to plan regular maintenance as the most cost-effective way to treat its streets, and engineers at DOT and its suppliers have fine-tuned it into a science-or art.
[[In-content Ad]]
