|Why do we need to evaluate pavements?
In general, pavements perform well for the first 75% of the life cycle, then deteriorate rapidly for the remainder of the life cycle. The length of time a pavement remains above the "good" condition level depends on the quality and timing of maintenance. Theoretically, given consistent loading patterns, a pavement system can be maintained at a "good" condition level indefinitely by properly timed and qualitatively controlled rehabilitation and maintenance operations. Therefore, for fiscal, safety, liability and life cycle reasons, it is critical that roadway pavements receive proper evaluations. The following maintenance strategies and generalized maintenance cycles were used to help establish a Pavement Management Program which also helps to address various Pavement Distress Types.
The current condition of County Roads based on most recent Route Evaluation Study is graphically shown below:
Pavement Management Program
According to recent studies by the Strategic Highway Research Program (SHRP) and the National Cooperative Highway Research Program (NCHRP), the most cost effective pavement strategy-which results in the highest pavement condition rating-is to perform preventive maintenance activities on the better rated pavements first, and then fund the rehabilitation of the poorer rated pavements. As such, any funding strategy that addresses the worst pavements first is the least cost effective. The objective of our Pavement Management Program (PMP) is to determine the most cost effective maintenance, rehabilitation and reconstruction strategy that provides the longest life for a roadway-and at the same time-costs the least. This is accomplished by identifying those roadways in most need of attention and developing a priority list to control the allocation of available funds. The resulting priority listing is defensible and generally eliminates questions of favoritism or bias. Residents often ask why their street is not being paved, while a nearby street in seemingly better condition is scheduled for maintenance. The following criteria may help to answer this question:
Cul-de-sacs usually have a lower priority than through streets since they do not serve as many houses and do not carry through traffic.
Arterial and collector streets usually receive maintenance when they appear to be in "good" condition. This is especially noticeable when compared to local streets, which are in worse condition visually. This is necessary because of the importance of these major streets in the overall traffic flow, and because of the heavy traffic loads they carry. A major street, which falls below a certain state of disrepair because of lack of funding, will not benefit from an overlay, and would not be an efficient use of the street funds. In these cases the entire street needs to be excavated out and replaced.
Some pavement distresses are more severe than others. For example, "Alligator" cracking is more severe than surface weathering and surface cracks, because it is caused by traffic loads and indicates structural failure of the asphalt. Our Pavement Management Program estimates what percentage of the distresses is environmental, and what percentage is load related. This means that two (2) roadways with the same apparent condition may have different degrees of load and environmental distresses. The street with the higher percentage of load distresses should warrant some type of maintenance treatment sooner.
Funding has not been available to bring all of the County maintained roadways in St. Mary’s up to an "acceptable" level.
A pilot project was completed in May 1999 which included an evaluation of 41 County-maintained roadway segments covering approximately 45 miles. The Engineering Division performed independent field inspections and identified fifteen (15) types of pavement distress which were rated according to their severity. The results were used in calculating an Overall Conditions Index (OCI) for each roadway and developing a formal Rating System for use on all other County roads. In general, we will be able to better quantify and predict which roads are in need of routine maintenance (patching, crack sealing etc), preventive maintenance (surface sealants), rehabilitation (overlays and surface treatments), reconstruction (widening, realignment etc) or deferred action (Between preventive and rehabilitation). Existing pavement conditions will be rated annually in preparation for the submission of the multi-year Capital Improvement Plan.
A certified transportation consultant performed a visual site investigation of the entire St. Mary’s County public road network as a part of a formal Route Evaluation Study which was completed in October 2002. The results were compiled using Cartegraph Road Inventory software. The data collected was based on an overall general observation and condition assessment rating of the physical features of the roadway; average daily traffic, distress, geometrics, ride, width, shoulder width and safety and to supplement the Department’s Road Data Index. Inspection categories were assigned a value between 0-failure and 100-excellent and included pavement condition, markings, geometry, rideability, volume, safety / roadside hazards, traffic signage, etc.
A rating system was subsequently developed to determine priority levels for specific capital roadway improvements by identifying critical roadway characteristics which effect travel safety, operation and driver convenience. The results of the cumulative rating will be used to assist in the decision making for the ongoing improvement, maintenance, rehabilitation and reconstruction activities. The Route Improvement Program is comprised of a Pavement Management Program (PMP) and Safety Improvement Program (SIP). Based on the Overall Rating and MRR strategy, it was determined that; approximately 18% of our roadways require no maintenance (rating 91-100) at this time, 73% require programmed routine maintenance (rating 76-90), 5% require rehabilitation (rating 70-75) and 4% reconstruction (rating 0-70). In short, about 78% of our roadways fall under the routine maintenance category.
Field Evaluation Table
Local officials, chronically short of resources and expertise can protect themselves by demonstrating that: (1) They have identified safety problems on their roadways and formulated solutions for them, and (2) They have moved with reasonable speed to correct those problems. The first step, is planning / inventorying the road system, identifying problem areas, and developing a plan or programs to remedy those problems.