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Pavement Preservation

In the fall of 2015, a pilot road resurfacing product was tested in four distinct neighborhoods within Mukilteo.  By working together with the County, a material called Ultra-Thin Bonded Wearing Course, or BWC, was applied to resurface 4.7 miles of streets in these areas. You may have heard of Chip Seal, a method the City used from 2007-2013. In 2014, Mayor Gregerson directed staff to stop using chip seal, and to investigate new techniques that could deliver higher quality to our neighborhoods.  We searched for other methods that could resolve the concerns associated with Chip Seal’s rocky surface, while still preserving the street infrastructure at an affordable price.  BWC is a mid-range technique that is being piloted not only in Mukilteo, but also in Marysville, Mill Creek and Snohomish County.  Working with our neighbors helps bring costs down, BWC has a longer life span than Chip Seal and the finished surface should feel almost like new asphalt. The cost is more expensive than Chip Seal; however, the City anticipates the longer life-span and smoother finished surface will provide the level of service that residents have requested.

In addition to resurfacing the streets, non-compliant curb ramps will be replaced in order to meet the requirements of the Americans with Disabilities Act.   Street maintenance is important because it prolongs the life of a street and saves money by improving the street before it reaches the point where very expensive full reconstruction is required.

How is the City paying for this pilot project?

This project is being funded via real estate excise taxes- taxes collected from home sales.

History of Pavement Preservation in Mukilteo

Mukilteo, as with most Cities, uses a commercially developed Pavement Management System (PMS) that is normally updated every 3-4 years.  The core of the system is pavement surface quality ratings for every street in the City other than the State highways which remain a responsibility of the State Department of Transportation.  From that the system recommends a program of annual expenditures that will help maintain good quality streets at that level or higher by preventing or reducing the wear from weather and vehicles.  A common question is “why are you spending money on that street, it looks fine?”  The answer is that to keep it looking fine its surface needs to be maintained.  Failure to maintain the surface leads to failure of the entire layer of pavement and sometimes the subsurface base, forcing the replacement of the entire pavement layer with new asphalt – an expensive process.  An easy way to think of pavement (asphalt) preservation is to liken it to changing engine oil in your car.  If you change the oil on reasonable recommended schedule, generally, the engine will last a long time.  The same goes for a properly built street – with a refresher coat every 7-10 years it will last twice as long as normal.

Mukilteo is fortunate in that current street ratings are relatively high with overall rating of very good (the Pavement Condition Index is 79 out of 100).  This is good news in that streets rated down to a PCI of about 55 (low end of the “Good” rating) allows the use of pavement preservation processes (seal coats). Below that PCI the pavement may need to be replaced.   A PCI of “0”  would be considered a gravel street, while a PCI of “100” is a newly paved street.  See the current street rating map (Click here to view map).  In looking at the map and comparing it with what you are used to driving you may find a few street sections around the City that the PMS program rates higher than it appears they should be.  This can be attributed anomalies in the rating process – however while not a perfect system the ratings are fairly accurate.

Streets in the 60-80 (Good to middle of Very Good) range may have some cracks but generally, more than anything else, will be suffering from oxidation (break-down) of the top surface.  This leads to hairline crack formation which allows the entrance of water into and below the pavement, leading to a shortened pavement life and early failure of the pavement subgrade base.  Seal coating restores the oxidized surface and seals the pavement to prevent water entrance as well as adding a new wear course and adding improved traction (a good thing in wet and frosty conditions).

It is also important to evaluate pavement preservation from an environmental standpoint (the Green viewpoint).  Seal coats such as chip seals are more environmentally sound than paving.  Three applications of chip seals over a 30 year period will use less than half the rock and oil of a conventional asphalt overlay.  Ultimately, use of chip seal as a alternative in Mukilteo was rejected, and use of BWC is hopefully a much more long-term and successful product.


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