Like many other components of our national infrastructure, streets and roads do not get much attention until there is a problem. Funding limitations often force counties, municipalities, and university campuses to put off routine maintenance of asphalt surfaces until such problems exist to the point that major reconstruction of a road, street, or parking lot is necessary. Research has shown that it is far less expensive to keep a road in good condition than it is to repair it once it has failed. In addition to the cost of major repairs, pavement in poor condition causes increased fuel use, vehicle wear and tear, and is detrimental to safe travel. One of the most underutilized tools in identifying developing problems and prioritizing maintenance schedules to extend the life of pavement surfaces is the implementation of a Pavement Management System.
A Pavement Management System consists of three major components:
- A system to regularly collect pavement condition data.
- A method to sort and store the collected data.
- An analysis to evaluate repair or preservation strategies and suggest cost-effective projects to maintain street conditions.
Larger cities may have the budget to dedicate full-time staff and use commercial software to manage their municipal pavement system. These systems facilitate the collection of Pavement Condition Assessment ratings, assist in prioritizing and tracking maintenance and repairs, track expenditures, and assist with annual budgeting.
Pavement condition data collection methods range from simple “windshield surveys” to the use of elaborate testing vehicles that measure smoothness, skid resistance, faulting, and cracking in the road surface. From this assessment, pavements are typically given a rating or grade that is used to rank order the condition of streets.
For smaller municipalities with limited budgets, city staff can conduct Pavement Condition Assessments (PCA) of existing streets. A PCA can be conducted in a low-cost manner to evaluate the existing condition of pavement surfaces without the use of expensive testing equipment that is not readily available to smaller municipalities. Such rating systems allow engineers, public works directors, street department superintendents, and physical plant directors to assess the current conditions of the pavement surfaces and address potential issues before they become major failures. The system can also be used to prioritize surface rehabilitation efforts for a city, county, or campus.
The process is quite simple and can be performed in-house or through the services of an outside engineering firm. The complexity of the project depends on the size of the municipality and the number of miles of streets to be evaluated.
Under a typical system, an inspector begins by preparing a map of the streets to be evaluated so that progress can be tracked. The inspector then slowly drives each section of street to produce an overall rating of the ride quality (smoothness) of the road on a scale of 0 to 10 with 0 being an excellent, smooth surface and 10 being the worst. Then, to get a closer look, the inspector walks each section, taking notes of the various types of failures and distress of the pavement, giving a numerical value for each distress or failure noted. Since most streets in Arkansas and Oklahoma are constructed with asphalt (vs. concrete), following are some of the typical asphalt distresses seen in local pavements:
Transverse Cracking – Cracks that occur roughly perpendicular to the centerline, usually a result of surface shrinking of the asphalt layer or reflection of existing cracks in underlying asphalt layers.
Longitudinal Cracking - Cracks that run parallel to the centerline and are usually a result of poor joint construction, or surface shrinking similar to transverse cracks.
Shrinkage Cracking – Cracks that appear on the pavement surface as interconnected cracks, forming a series of polygons. Much like transverse and longitudinal cracking, these cracks can be a result of surface shrinking caused by weather cycles, or heaving in the aggregate base or subgrade.
Alligator Cracking – These are interconnected cracks that form a series of small polygons that resemble the skin of an alligator. These cracks are typically signs of failure in the aggregate base or subgrade caused by poor drainage combined with heavy traffic load.
Raveling – The deterioration of pavement by the loss of asphalt and rock. Such deterioration can be a result of poor compaction at the time of construction, aggregate separation due to a poor mix from the asphalt plant, or the dislodging of aggregate materials in high-traffic areas.
Rutting – The permanent deformation of asphalt surfaces over time, usually shown by the depression of the wheel paths in the roadway. This failure is typically the result of poor compaction during construction, improper mix design for given traffic conditions, or failures in the subgrade or aggregate base course.
Potholes – A depression in the asphalt surface that is the result of the removal of broken pieces of pavement. They are formed as a result of expansion and contraction during freeze-thaw weather and water cycles combined with the amount of traffic load on the pavement. A pothole is typically the end result of other failures mentioned above that have not been corrected.
Other distress symptoms include corrugation, shoving or pushing, and excessive asphalt.
Once all of the evident distresses are noted and a numerical value assigned, the totals are added and the sum is subtracted from 100 to give a Pavement Condition Rating (PCR). For example, if a particular ½ mile of street was noted to have 6 or 8 transverse cracks, some longitudinal cracking, moderate shrinkage cracking, and two areas of alligator cracking, then the total deficiency value would likely be in the 20 to 25 point range. Subtracting this total from 100 produces a PCR of 75 to 80. A rating in this range typically means that the lifespan of the asphalt surface could be extended by sealing the cracks and applying an emulsified asphalt seal coat, or microsurfacing course.
Roads with PCRs of 60 to 75 may require more extensive repairs such as full depth patching and overlays, while roads with ratings below 60 typically require reconstruction. Obviously, a road or street with a rating of 90 to 100 is considered in good shape and little or no immediate attention is needed.
Once each street in the study has been rated, the results can then be tabulated and prioritized to develop a maintenance schedule based upon the street maintenance budget. A prioritization factor can also be assigned to some streets that should have a higher priority such as those that serve as main gateways to a city or campus that are more utilized than other streets.
In conclusion, a good Pavement Management System is a valuable tool that can help municipalities or campuses maintain and extend the life of their pavement. Systematically identifying minor problems before they become more serious can decrease the frequency of costly pavement reconstruction projects.