Seattle street crews will spend the summer getting streets in North Seattle ready for another round of chip-sealing. But they'll hold off the block-by-block application of oil, chemicals and rocks until next year, according to Patricia Carroll, associate civil engineering specialist for the Seattle Department of Transportation. She helps manage the chip-sealing program.
The work is expected to begin today, July 7, in Haller Lake, between Northeast 135th Street to the north, Fifth Avenue Northeast on the east, Northgate Way on the south and Aurora Avenue North on the west.
"Chip-sealing creates a highly skid-resistant surface," according to the city's official chip-sealing website (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. Chip-sealing is cost-effective, and crews can resurface up to several miles of roadway in a day's time."
After making spot repairs, street crews will pour a special blend of polymer and liquid asphalt on selected streets, pour rocks that have been carefully sized to minimize flying into windshields and roll the mixture down.
A big money-saver
The program saves the City of Seattle 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, saving more than $243,000 per mile of two-lane road. (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 on the city's website that show that the city began converting dirt and gravel non-arterial streets to chip seal in 1967, 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.
Getting ready
A crew from the Northwest Center, a nonprofit organization working to provide opportunities of children and adults with disabilities, distributed blue-on-white door hangers explaining the chip seal program.
"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, the Northwest Center sent another crew out with fluorescent orange door hangers, advising residents that chip-sealing is imminent and not to drive faster than 10 mph 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 placed barricades and signs along the sides of the streets they will seal to prohibit parking. They also covered any storm drain inlets.
The big event
On the day of the sealing, a parade of equipment will line 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 will be from 7 a.m. to 6 p.m. Monday through Friday with traffic restrictions in place from 7 a.m. to 3:30 pm.
Just in case someone failed to heed the no-parking signs, city crews will mask car fenders or bumpers to avoid getting sprayed with the compound.
Right behind the oil truck, a rock spreader will come by, usually in tandem with a dump truck full of rock chips.
Crews operating power rollers will then tamp down the polymer-and-rock mixture, and a supervisor will follow closely in a pickup truck, 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 mph 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.
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