WAC 136-70 requires Washington State Counties to implement a pavement management system in order to be eligible for the County Arterial Preservation Program (CAPP), assuring that paved county arterial roads data is available to evaluate regional or statewide arterial preservation and rehabilitation needs.
Pavement Management System (PMS) is a methodology for maintaining road surfaces by systematically analyzing pavement life cycles and pavement ratings to determine timing of a pavement preservation, as well as the most cost effective pavement rehabilitation type. In addition, a PMS assists in developing pavement rehabilitation budgets that will prevent major road deterioration.
The roadway and pavement information is in the County Road Log, and updated annually as part of the Road Log update process. The Mobility PMS uses the Road Log information directly; counties using another PMS program have a routine to transfer the current Road Log information to their program.
There are three levels of work on pavements:
There are three phases in the life of a pavement:
The year the pavement reaches the should and must levels is critical. The "should" level is the PSC level where a rehabilitation should be considered. If the PSC is above the should level, there is still life available in the pavement, and rehabilitation is not yet cost effective. If PSC is below the "must" level, the pavement is in such a deteriorated condition that the road should be rebuilt and a surface rehabilitation will not be adequate to restore the road to its original condition. The should and must levels are selected by the user. Typically the should level is a PSC of 60 (representing a 40% drop in quality) and the must level is a PSC of 40.
By knowing when pavement preservation is cost effective, the county can spend their limited pavement preservation funds on the most cost-effective rehabilitations. By properly preserving their pavements, they reduce the need for and cost of routine pavement maintenance.
The results of the PMS program are not the final answer. The PMS results are but one of the items that must be considered during the engineering analysis of the proposed pavement preservation program. Each proposed project needs to be reviewed to make sure it is the right thing to do.
The PMS strategy applied in Mobility Pavement Management System consists of four major parts:
1. Surface Conditions – Recording visible distresses on the pavement surfaces, which are calculated into a Pavement Structural Condition (PSC) score. Alligator Cracking and Patching have the highest deductions. The top 4 core structural pavement defects are – Transverse cracking, Longitudinal cracking, Alligator cracking, and patching. At a minimum, counties are required to rate their Paved Arterial network (Arterial and Collector roads) every two years.
2. Generate Project File - Define a road system as a rational set of projects.
3. When Analysis - Formulate a Pavement Performance Curve to predict the PSC score for each project segment.
4. What Analysis - Define and apply a budget and strategy, comparing the results of multiple iterations to determine the best course of action.
Download the report that describes the four major parts of the MPMS strategy in detail.
A benefit of a Pavement Management System is the determination of whether a preservation activity will or will not be cost effective. One of the reports (Below Must) provided by the PMS is a list of all roads in such a poor condition that a preservation activity will not be cost effective, and that these roads need to be reconstructed. These roads need an in-depth engineering analysis to determine what should be done to improve the road. If reconstruction is needed, funds must be located, such as RAP funds for rural arterials, TIB funds for urban arterials, state and federal funds.
The use of a PMS to determine if a preservation project is cost effective does not prevent the county from doing non-cost effective preservation projects. If it is determined that a preservation activity will be done, for whatever reason, that project will be done. The PMS provides an engineering reason for not doing the project, such that the pavement is in such poor condition that a pavement preservation will not last and is not cost effective.
The roadway and pavement information is in the County Road Log, and is updated annually as part of the Road Log update process. The Mobility PMS uses the Road Log information directly; counties using another PMS program have a routine to transfer the current Road Log information to their program.
All county jurisdiction paved collectors and arterials, as defined by the most recently approved county Road Log as described in chapter WAC 136-60, shall be surveyed for visual pavement distress at least biennially. Distress rating information must be keyed to the County Road Log by both road number and mileposts. All visual distresses (or defects) for both flexible and rigid pavements, both in severity and extent, shall be as defined within the "Pavement Surface Condition Rating Manual" (March 1992, produced by the Washington state transportation center in cooperation with the northwest pavement management systems users group and the Washington state department of transportation). Only those distresses noted as "core program defect" are required to be surveyed.
Rating can be done by county personnel or by an automated pavement rating service. When county personnel do the visual rating, they usually drive the roads at low speed and rate the distresses. The time needed depends on the rating methodology and the number of miles to be rated. Depending on the number of miles rated, it will take anywhere from two weeks to one month. Numerous counties use computerized data collection, entering the data directly into a computer; counties using paper need to enter their data into the computer data base.
A critical step in building a PMS is to design a Decision Tree that best fits the county needs and expectations of the road network. A Decision Tree is basically a set of "Rules" by which each road segment is evaluated. A Rehabilitation Type, Rehabilitation Date, and Rehabilitation Costs are then calculated for each road segment based on the Decision Tree. A sample decision tree is pictured below.
Strong communication of need to decision makers and a long-term commitment is necessary to be successful. Failure to maintain a roadway network at the optimal time dramatically increases maintenance cost, decreases drivability and may expose the public to increased risk of higher accident rates. The cost of pavement preservation increases exponentially with pavement deterioration. Therefore, the three sound principles for pavement preservation should be followed - The Right Treatment, at The Right Time, on The Right Road.