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Pavement Preservation Options
Overview of City Roadway Network
The City of Mill Creek has 106 lane miles within city limits, which is about 875,000 square yards of pavement. The typical life expectancy of original pavement is about 30 to 40 years. City streets currently range in age from 10 years to 40 years. As pavement begins to deteriorate, the deterioration rate is not constant. While pavement holds up for most of its life expectancy, as it nears the end of its life, pavement life quickly deteriorates. The general concept of pavement preservation is that as pavement deteriorates, intervention is done at the proper time with some type of surface treatment that returns it to a like-new condition and extends the pavement life. The City’s goal is to intervene before roads deteriorate in order to preserve City infrastructure.

The use of surface preservation treatments have been part of the City’s ongoing Pavement Preservation Program. Chip seal has been used on an annual basis in Mill Creek since 2012, and has been applied in most of the 136th Street / Heatherwood West / Silver Crest neighborhood areas. It is a structurally sound pavement preservation approach, and has met all preservation goals to date. Recommendations for pavement preservation applications are based on the condition of the roadway, and the proposed work plan is approved by the City Council at the start of each year.

Recent Mill Creek Urban Chip Seal Overlays
  • 2012: 136th Street in front of Jackson High School.
  • 2013: Heatherwood West Neighborhood. 136th Street SE from Jackson High School to 27th Drive SE, around the loop to 28th Avenue SE and on 133rd Place SE.
  • 2014: Heatherwood West neighborhood from 136th Street SE down 25th Avenue SE and 26th Avenue SE, and along 139th Street SE / Silver Crest Drive.
  • 2015: Wexford Court neighborhood off 23rd Avenue SE.
  • 2016: Wildflower and Mill Park Village neighborhoods. 

Pavement Preservation Issue Summary
In fall 2016, the City of Mill Creek contracted with Snohomish County as part of its interlocal agreement to apply a chip seal treatment to preserve the roadway surface in Mill Creek’s Wildflower and Mill Park Village neighborhoods. Shortly afterward, the Mill Creek Community Association contacted the City about concerns from its members over the use of the chip seal process for roadway surface preservation within the City of Mill Creek. Residents noted that the pavement surface was not even; the application of chip seal was not cleanly done, covering some curb cement or leaving gaps between the roadway and the curb; and in some instances, the application was uneven in the middle of the street, leaving lines. In addition, it was noted that during the application of chip seal in a portion of the Heatherwood West neighborhood in 2014, an unexpected rainfall occurred, which left some blotches in the pavement aesthetic.

While the structural integrity of the roadway was improved by the application of chip seal, the application has had undesirable aesthetic impacts to neighborhoods. At stake are three issues:

  1. Maintaining City infrastructure.
  2. Preserving the community aesthetic.
  3. Achieving the first two items in a fiscally responsible manner.

The City takes very seriously the importance of maintaining the aesthetics of the City. As part of the City’s guiding principles, City staff support the development, maintenance and revitalization of public and private property to ensure the continuation of Mill Creek as a safe, clean and well-maintained community. In addition, the City is committed to fiscal responsibility, managing the City’s financial resources to provide quality public services, cultivate economic prosperity and maintain a sustainable budget.

These principles are pitted against one another in this situation. The issue of pavement preservation is a larger policy issue for the City and has significant financial implications. Therefore, the City Council must carefully decide how the City will move forward.

Among the points of consideration are these:
  • How does the City ensure all concerns from residents are treated equally?
  • How can the City ensure it doesn’t respond arbitrarily?
  • What are the criteria for “redoing” chip seal applications with overlay?
  • Is there a way to move forward in a fiscally responsible manner that achieves customer satisfaction?

Overview of Pavement Preservation / Reconstruction Options
There are three pavement preservation / reconstruction options.

  • Chip Seal is a very cost-effective surface preservation treatment for roadways that are still in good condition, and can extend the life of the pavement for seven to 10 years. It is generally applied to roads that are still structurally sound, providing a protective coating on the top. The chip seal process consists of an application of a thin hot liquid asphalt film that is then covered by a layer of crushed rock. The chips are immediately compacted into the roadway for maximum adherence, and excess rock is swept up. After a few days a top coating of liquid asphalt is applied to seal the surface and to help keep the rocks in place.
Chip seal is one of two locally available surface preservation techniques, which are used to extend the service life of a roadway that is in good structural condition. The cost of a chip seal preservation treatment is typically $3-$5 per square yard for total project cost. Its advantages include minimized construction impacts and that it hides surface flaws. Urban chip seal overlays are significantly less expensive than hot asphalt overlays. One reason for this is that the U.S. Department of Transportation requires American Disability Act sidewalk ramp upgrades when new asphalt overlays are applied. A disadvantage is that the application is not always aesthetically pleasing, especially on roadways with curves; it is best applied on straight roadways.

  • Slurry Seal: The other potential preservation method is a slurry seal and can extend the life of the pavement for seven to 10 years. While the cost per square yard is comparable at $2-$4, it brings has several disadvantages and requirements for which the City of Mill Creek has not recommended its use. This includes the potential for the pavement surface and any flaws to show through. In addition, because it isn’t widely used, the outcome of the finished product is unknown. It also has greater construction impacts during the day because the treatment needs to cure, so the neighborhood cannot access the street at all until it’s complete. This application requires a large-scale project to make it worthwhile for a contractor to complete the treatment.
Therefore, the cost of this application for the Wildflower and Mill Park Village neighborhoods along with the minimum project scale is at least $150,000.

  • Grind and Overlay: A third pavement alternative is overlay, in which the pavement is ground down and new pavement applied. This generally is only done when there is a structural failure on the top layer of the roadway; it is a structural replacement. This is very costly, at approximately $25-$40 per square yard. While costly, the new roadway should last 20-30 years. This process, however, also requires ADA ramp upgrades, including engineering design and construction, which could easily add $8K - $10K to project costs per ramp.
To overlay the Wildflower and Mill Park Village neighborhoods alone it is estimated to cost $250,000. Adding in the Heatherwood West neighborhood would increase costs to $1.5 million to $2 million.

City Council Information and Decisions
Map of Chip Seal Applications in Recent Years
A map of chip seal applications.
In response to the concerns raised by Mill Creek residents, City Manager Rebecca Polizzotto suspended urban chip seal road overlays at the City Council meeting on Oct. 4, 2016, while the City Council considers options for pavement preservation work. To achieve this, the City Council has directed staff to investigate two items.

  1. Pavement preservation options and costs.
  2. How to resolve the issue presented in the Wildflower and Mill Park Village neighborhoods, and on 26th Avenue SE in the Heatherwood West neighborhood.

On Jan. 24, Public Works Director Scott Smith presented application options. See the presentation.

On Feb. 14, Smith presented cost comparisons to help the City Council understand costs of addressing immediate concerns and long-term fiscal implications for moving to an overlay approach. See the presentation.

City staff prepared additional information for the March 7 City Council meeting, including firm costs for addressing the Wildflower, Mill Park Village, and Heatherwood West neighborhoods; a tentative list of upcoming projects; and life cycle cost estimates for various pavement preservation options. Listen to the discussion.

The City Council made the decision at its March 14 meeting to move forward with overlay work in four neighborhoods: Wildflower and Mill Park Village neighborhoods, as well as two Heatherwood West neighborhoods, including 26th Avenue SE and the "Racetrack" area comprising 27th Drive SE and 28th Avenue SE. See the full press release.

Next Steps
As part of the work plan for the 2017-2018 biennium, City staff will develop a comprehensive update to the City’s Capital Improvement Plan (CIP). Among those projects, the City is exploring pavement preservation alternatives that help maintain the City’s infrastructure in the most fiscally responsible manner. This includes an updated analysis of all pavement preservation needs, treatment options, costs and funding sources. In addition, measures will be instituted that ensure quality control of work performed by contracted and interlocal partners.

This CIP work and funding options will include significant opportunity for community input, as well as community participation in the prioritization of capital projects.