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Pavement Condition

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Pavement Condition
Tigard's 148-mile paved street network represents an investment of over $140 million, with an additional $120 million invested in curbing, sidewalks, drainage, and right-of-way. The City's street infrastructure represents the largest investment owned by Tigard citizens, and the overall pavement condition represents the health of this network.

Pavement Rating System
Pavement health is measured by a Pavement Condition Index (PCI). The PCI indicates the extent and severity of pavement distress such as cracking, rutting, raveling, etc. It is expressed as a number from 0 (very bad, essentially gravel) to 100 (essentially perfect). New streets start with pavement conditions in the high nineties. For ease of understanding, pavement condition is often classified as follows:

Very Good (85 to 100)
Good (70 to 85)
Fair (55 to 70)
Poor (40 to 55)
Very Poor (Less Than 40)

Current Conditions in Tigard
The City completed a Pavement Management Analysis report re-rating all City streets, and providing a PCI rating for each street.

Today, Tigard's streets are in fairly good condition. The network average is an overall condition rating of 68 and the backlog of preventative maintenance is at 10%. However, there is cause for concern with 45% of the streets in the acceptable and fair categories. This means many streets will become reconstruction candidates in the next five to ten years. A preventative maintenance approach is needed to stop this trend.

A graph showing pavement condition in Tigard by type of street and percentage of network by area is available here. A map showing pavement conditions throughout the City is available here.

Condition Examples
To give you an idea of what a street in very good condition versus fair condition actually looks like, City staff prepared a presentation showing examples of pavement condition throughout the City.

The presentation includes:

79th Avenue north of Durham Rd; Paved in 2008; PCI of 95
108th Avenue south of Durham Rd; Paved in 2007; PCI of 93
Commercial Street between 96th Avenue and 97th Avenue; PCI of 78
Tigard Street near Fanno Creek; PCI of 72
Bonita Road between Hall Blvd and 79th Ave; PCI of 72
72nd Avenue between Redwood Ln and Cardinal Ln; PCI of 64
Commercial Street west of Main St and Hwy 99W Overpass; PCI of 52
Commercial Street east of Main Street; PCI of 42
98th Avenue south of Greenberg Rd; PCI of 34
Beveland St east of 72nd Avenue; PCI of 20

Factors Affecting Pavement Condition
The primary factors causing pavement deterioration are the vehicles that travel over the pavement. These factors include:

Traffic volume;
Volume of trucks and other heavy vehicles - the pavement deterioration caused by a vehicle increases exponentially with the amount of weight on each axle; and,
Vehicles accelerating, braking, and turning which exerts more force on the pavement, and accelerates pavement deterioration. This is why pavement deteriorates faster near intersections and in sharp curves.

Other factors include:

Weather (which is the primary cause of decay on streets with very little traffic volume) - especially rain and freeze/thaw action;
Settling of the ground beneath the pavement - especially soils with high clay content; and,
Construction and or utility work that necessitates cutting into the pavement to access a utility line.

Examples of pavement deterioration include:

Rutting - When pavement surface becomes depressed along the wheel paths
Longitudinal Cracking - cracking along the roadway, parallel to the direction of travel
Transverse Cracking - cracking across the roadway, perpendicular to the direction of travel
Alligator Cracking - a combination of longitudinal and transverse cracking that has become so dense it resembles alligator scales
Loss of Fines - when the cohesive material near the top of the pavement wears away, often due to weather or traffic loading
Raveling - (perhaps better called unraveling) - When pieces of aggregate come out of the pavement as it continues to lose its fines
Pumping - when liquids (such as water or liquid asphalt) are drawn to the surface (so it looks like the road is pumping out the liquid)

Street Lifecycle
Streets are designed to last about 20 years, but the pavement begins to deteriorate much earlier. Studies have shown that pavement health worsens at an increasing rate as the pavement gets older.

Without periodic, preventive maintenance, a street's condition deteriorates 40% in the first 15 years of its life. Then over the next 5 years, the street will greatly deteriorate, requiring major reconstruction.

Preventive maintenance using cost-effective ($1.60 to $13/sq. yd.) slurry seals or 2 to 3-inch overlays during the first 10 to 15 years can extend a pavement life to 30 years and more. Without these surface treatments, costly reconstruction is required ($35 to $55/sq. yd.).

Tigard Street Maintenance Update

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