Pavement Condition Index
In 2010, the City collected pavement condition data as part of the Mobile Asset Data Collection project to assist staff in developing priorities for maintaining and improving City streets in a more proactive manner. Part of the Mobile Asset Data Collection project was to inspect the City’s public streets using high-resolution oblique imagery and use that data to quantify the type, severity and extent of pavement distresses. This information is now used by staff to calculate a pavement condition rating for the 80 miles of the City’s public streets.
Streets begin to deteriorate from the moment they are constructed. There are several factors that affect pavement life, which makes it difficult to predict exactly how long a street will last before it will need to be resurfaced or rebuilt. Streets, with higher traffic volumes and with vehicles carrying heavy loads (typically arterial streets), will deteriorate more quickly than less traveled streets. Weather (rain, extreme heat or cold) can greatly affect pavement performance. In addition, the base material and underlying soil supporting the roadway, the type of pavement (concrete versus asphalt) and the age of pavement all play a part in how long the pavement surface will last.
Industry standard suggests that an average pavement life is 18 years before there is a significant drop in condition. Mercer Island’s streets history suggests that the life of arterials averages 25 years and the life of residential streets averages 35 years.
Regular assessment of the ‘state of our streets’ will help staff track pavement condition and chart pavement trends to support funding levels into the future for street resurfacing projects. An ongoing program of inspection utilizing a Mobile Asset Data Collection system will continue to build a stronger pavement management program.
Rating the Pavement Conditions
Staff uses the pavement condition ratings to rank streets on a 100-point scale, with excellent streets rated at 100 and failed streets rated 0. This allows for better identification and tracking of the number of streets that only need minor repairs to maintain their high rating, the number of streets that are approaching their life expectancy and are in need of some type of resurfacing, and those streets that are past their life expectancy and are in need of substantial repair prior to resurfacing. This data provides a financing plan to provide for long-range capital reinvestment in the roadway system.
Future collection of pavement distress data at regular intervals will show which streets are deteriorating and how quickly and which streets are maintaining their good conditions over time. Information and Geographic Services (IGS) and engineering staff will continue to develop a ‘streets’ database within the City’s GIS network (similar to those developed for the water, sewer and storm drainage utilities) using the current Mobile Asset Data Collection information as well as historical data. With this information, staff will be able to transition away from a pavement life range towards a more specific lifespan target.
Current Road Distresses
This map shows the Pavement Condition Index (PCI) for arterial streets in summer 2013.
This map shows the Pavement Condition Index (PCI) for residential streets in summer 2013.
Click here to view Agenda Bill 4928: Transportation and Street Fund Policy and Budget Issues as presented at the February 24, 2014 Study Session
Click here to view the PowerPoint presentation on Pavement Condition Ratings from the February 24, 2014 Study Session.