Pavement Management
|
| The
Washington State Department of Transportation (WSDOT) route system
accommodated 52 billion vehicle-miles of travel during 1997.
This amount of travel represents vehicle operating costs of
about $23 billion to the traveling public.
The WSDOT annual budget without the ferries, aviation, and
state interest programs amounts to an expenditure of 1.9 cents per
vehicle-mile traveled for a total of $900 million.
Thus, WSDOT spends for pavements about one cent for every 30
cents spent by motorists for their vehicles.
Based on national averages, every person travels about 30 miles
per day (mostly on highways) for a total daily expense of about $15.
If state highway pavements become rougher, motorists’ vehicle
operating costs will increase. Providing
and maintaining pavements is expensive and important—both to
motorists and WSDOT.
|
|
Bituminous Surface Treatment
Pavement
|
All
hard surfaced pavements can be categorized into two groups: flexible
and rigid. Flexible
pavements are those which are surfaced with bituminous (asphalt)
materials in the surface course (often referred to as the wearing
course). These can be
either in the form of pavement surfaces such as a bituminous surface
treatment or asphalt concrete. A
bituminous surface treatment is used on
|
| lower
traffic volume roads (generally less than 2,000 vehicles per day) and
asphalt concrete surfaces for higher traffic conditions.
Rigid pavements are composed of a Portland cement concrete
surface course.
|
| Asphalt
surfaced pavements require resurfacing every 10 to 15 years; concrete
pavements can last up to 30 years or more before major rehabilitation
is required. Generally, it is quicker and less expensive to
rehabilitate asphalt concrete pavements than concrete pavements but
the rehabilitation does not last as long.
There are tradeoffs with each.
|
Asphalt Concrete Pavement
|
|
The WSDOT route
system has about 17,900 lane-miles of pavements.
A breakdown by pavement type includes:
-
Asphalt
Concrete Pavement:
10,776 lane-miles (60% of network)
-
Bituminous
Surface Treatment:
4,843 lane-miles (27% of network)
-
Concrete
Pavement:
2,262 lane-miles (13% of network)
|
|
Concrete Pavement
|
Clearly
the dominant surface type is asphalt concrete followed by bituminous
surface treatments and Portland cement concrete.
Further about 88 percent of the bituminous surface treatment
pavements are in the three Eastern Washington Regions, along with 36
percent of the asphalt concrete pavements and 40 percent of the
concrete pavement.
|
| Pavement
issues also relate to the more than 3,000 bridges that are part of the
aforementioned surfaces. Specific
Regional pavement type mile values are illustrated on the following
map:
|
|
WSDOT
Regional Lane - Miles
|
- WSPMS
- Software Guide
- System
Condition
- Structural
- Rutting
- Roughness
- Surface Friction
|
Structural Condition
Overall
pavement distress is termed Pavement Structural Condition (PSC) and is
calculated separately for flexible and rigid pavements. The PSC has an
upper limit of 100 (no distress) and a lower limit of zero (extensive
distress). The PSC is calculated based on the amount and severity of
the following distress types:
Flexible
Pavements
|
Rigid
Pavements
|
|
|
-
slab cracking
-
joint and crack spalling
-
pumping and blowing
-
faulting and settlement
-
patching
-
raveling and scaling
|
|
| For all route
classifications (Interstate, Principal Arterial, Minor Arterial, and
Major Collector) the overall PSC are shown below from 1971 to 1998. It
is notable how this condition measure has improved since
1971—noteworthy is the reduction of those pavements being in the
very poor category from about 20 percent of the total lane-miles in
the early 1970’s down to about one percent in 1994 and later.
The
concept of lowest life cycle programming proposes that the pavement
structural condition will approach an optimal condition. This
condition would result in an average statewide PSC value of about 81;
there would be no "very poor" or "poor" pavement
sections and the makeup of the system would be 25% "good"
and 75% "very good". WSDOT is making progress towards
this goal, albeit slowly.
|
|
Pavement Condition and Required Overlay
Thickness
The
figure above illustrates the required overlay thickness for the
various ranges of pavement condition. As a pavement becomes more
distressed (decrease in condition), an increase in pavement repair and
overlay depths are required. The lowest life cycle cost is obtained by
rehabilitating the pavement in the early stages of distress to reduce
the need for extensive pavement repair and thicker overlays.
|
| The
illustration below further details the PSC breakout for the 2002 survey year.
|
|
|
