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Street Maintenance Program
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 2007 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 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.
Preservation of the pavement quality by seal coating using the chip seal process was initiated last year on Harbour Heights Parkway. This half mile of collector arterial was chip sealed over a two day process. If it had been repaved, it would have taken two weeks. Sweeping of loose gravel begins immediately after the chip is laid down eliminating the need to close the road to traffic. A final top coat of light oil is placed on the chip a few days after the chip is laid down, locking down any remaining loose chips. The chip used is a doubly washed chip which virtually eliminates dust issues. While seal coating has been practiced all around the world for over 30 years, it has only been common in western Washington in the last 15 years, and mainly in southwestern Washington (Vancouver and Olympia). As the quality of rock, oil and equipment improved over the last ten years, so has the use increased, especially in urban setting.
And last, but not least there is the cost consideration. Seal coating versus paving, besides delivering a more consistent year to year higher overall quality of street surface, also delivers a substantial savings to the taxpayers. Repaving of a typical residential street with three inches of pavement, in 2008 dollars runs the range of $25 35/square yard, depending on the complexity of the project and whether the work can be done under a County contract or is done by a private contract, with the County contract being the least cost (the work is still done by the private industry, just under a very large County repaving contract). In comparison, chip seal runs $3-3.50/square yard. In a 30 year life cycle (assuming three chip seals) that translates to as much as a 71% savings. Savings sorely needed to rebuilt streets that have failed, improve substandard width streets, put in sidewalks and take care of aging traffic signals.
For additional information regarding this program,
contact Public Works Director Rob McGaughey at 425.263.8000.