Annual SDOT Microsurfacing Project
What is Microsurfacing?
Microsurfacing is a protective seal coat which extends the life of pavement. It is a thin, tough layer of asphalt emulsion blended with finely crushed stone for traction.
This is a cost-effective method to renew the road surface and seal minor cracks and other irregularities. This preventive maintenance process protects the pavement from moisture penetration and oxidation.
Similar to painting a house, microsurfacing creates a protective layer which preserves the underlying structure and prevents the need for more expensive repairs in the future.Microsurfacing is seeing growing use by transportation agencies, including SDOT.
An Alternative to Chip Sealing
In the past, SDOT’s primary method of preventive maintenance has been chip sealing. While chip sealing is an effective preventive maintenance measure, it leaves the roads very rough and there is an extended period of loose rock on the street. Microsurfacing and chip sealing are both seal coats that extend the life of the pavement for about the same amount of time (5 to 10 years).
However, microsurfacing has two key advantages over chip sealing:
Chip sealing has the advantage that you can drive on the street immediately, but with microsurfacing you must wait two hours or more for the surface to cure before driving or walking on it.
In 2013, SDOT conducted a pilot microsurfacing project in the Wedgwood neighborhood. Based on the results of that project, SDOT will microsurface selected blocks in Arbor Heights and Fauntleroy in 2014.
How does SDOT select the streets for treatment?
In the 1950’s and 1960’s, the City of Seattle annexed several parts of King County. Most of these streets had a dirt or gravel surface. The City paved these streets with a minimal amount of asphalt and began a regular preventive maintenance cycle, typically chip sealing the streets on a 10 year cycle.
Because these streets are mostly low volume non-arterial streets and have received preventive maintenance in the past, they continue to be the best candidates to receive preventive maintenance.
All the blocks resurfaced in a microsurfacing project are selected based on the age of the current pavement and an on-site inspection by SDOT staff.
Our street looks fine. Why resurface it?
Flexible pavements (typically asphalt) need periodic resealing to protect them from the deteriorating effects of water (rain) and sun. If left untreated, the surface becomes brittle and may crack and ravel. Periodic resealing prevents more extensive and costly repairs. Regular preventive maintenance is the most cost-effective way to maintain streets.
Preparing the street: fixing potholes, cracks, etc.
It is essential that structural damage is repaired prior to the microsurfacing process. SDOT crews will begin to patch deteriorated areas of the selected roads well in advance of the microsurfacing operation.
In addition, low hanging branches and overgrowth may need to be trimmed to allow for the microsurfacing equipment to navigate the roads.
On the day of microsurfacing, crews will sweep the street before applying the microsurfacing material.
The Microsurfacing Process
Microsurfacing is a process similar to a slurry seal. A mixture of asphalt emulsion and aggregate (crushed stone, gravel and sand) is applied to the road. However, unlike a slurry seal, microsurfacing uses emulsion that is modified with polymers and other ingredients so it cures more quickly.
As shown in this short video, as the microsurfacing equipment moves along the street, the mixture is fed into a spreader box. The material is spread across the full width of a traffic lane and then smoothed by a squeegee. The equipment also feathers the edges for a smooth transition. All this happens in one step. Here’s a very short video showing microsurfacing on a Seattle street in 2013.
After the microsurfacing seal coat cures (hardens), the street can be reopened and used normally. However, there may be parking restrictions and road closures for the entire day the work is scheduled. See details below under “How Residents May Be Affected During Microsurfacing.”
In the summer of 2014 SDOT will microsurface selected blocks in Arbor Heights and Fauntleroy.
Prior to the seal coat phase of the project, SDOT will determine which blocks will be microsurfaced, provide a specific schedule for the work and notify the neighborhood.
The 2014 project is bounded roughly by:
For a map of the 2014 project area, click here.
January – Summer of 2014: Preparation
Summer 2014: Seal Coating Work
ONE DAY ROAD CLOSURES
On the scheduled date of seal coat work, the full width of the block will typically be closed for two to three hours. During this closure time the contractor will sweep, apply the microsurfacing seal coat, and allow the microsurfacing to cure.
If you need to access your car, it's best to park it on another street for the day.
Wait to Use the Street
It typically takes about two hours for the microsurfacing to cure. No parking and road closed signs will be removed as soon as the contractor believes it is safe to travel on the road. In addition to vehicular traffic, you should refrain from walking, biking or bringing pets on the street.
No parking signs will be installed at least 72 hours before the start of work. On the day a block is scheduled for work, residents will not be allowed to park on the street.
No Driveway Access
Driveway access will be blocked for up to two hours. Once the microsurfacing is placed there is no access out of or into driveways during the curing period. Because we do not know in advance what part of the day this period would occur, if you need your car during that day, SDOT recommends parking on a block that is not scheduled for microsurfacing on that day.
Garbage, Yard Waste and Recycling Collection
If the microsurfacing project is scheduled on a day when solid waste is normally picked up on a particular block, SDOT will coordinate to have solid waste picked up during a specific period of time during that day.
Some blocks NOT receiving microsurfacing may be affected
On the day of the work, adjacent blocks may have more cars parked on the street and residents may need to navigate around the closed streets.
Access on a small number of adjacent blocks may be impacted at a similar level to access on the blocks receiving microsurfacing.
It Could be a Rough Road for a Bit
In general, right after microsurfacing, the road may have a slightly coarse driving surface. As cars drive over the road, however, the surface will become smoother, but still have enough traction to provide skid resistance.
SDOT appreciates the cooperation and efforts of residents and others who are affected by street maintenance projects.
We welcome your questions and comments.
For Street Maintenance 24-hour emergencies, please call: 206-386-1218.