Pavement Management is a challenging program for any community, complicated by the need to evaluate the best use of limited funds that are available. Municipal roads are not typically constructed to support the high traffic volumes and truck weights experienced by State DOT roads and highways, therefore local road design standards are different. In BSL many of our roads are either older, or were constructed without enough base materials to support heavy traffic. So our Pavement Management program needs to address both new roadway paving and the repair of distressed sections.
It is a common misconception that roadway performance and longevity is governed only by the surface materials (the asphalt pavement). That’s just what people see. Instead every road should be thought of as a composite system, consisting of asphalt pavement, subbase gravels, subgrade (natural existing soils) and in some cases a subsurface drainage system. Depending on soil conditions, traffic type and frequency, multiple layers of each component may be designed.
Significant strength and support is provided by the compacted layer of subbase materials which underlie pavement and should be well graded, free-draining gravels. The subbase gravel layer is the key to longevity, as it provides structural support and a means for subsurface water to escape. Without a good base, wet conditions are subject to freeze-thaw cycles and softened conditions that can cause rutting and potholes.
For every new road constructed in BSL, we are placing a properly compacted, free-draining subbase material to provide proper pavement support for long lasting performance. To minimize the City’s cost, our Public Works Department purchases and spreads this material in advance of the work by paving contractors. This ensures that the subbase is located correctly and is placed with adequate thickness. We also grade the area down in advance so that the new road is not significantly higher than the previous roadway.
New roads are constructed with a crown or high point in the middle, to promote surface drainage to the outside edges of the road. Ideally this water flows into our stormwater ditches and away from the roadway subbase. We do not have a curb and gutter system as shown in the example sketch below.
Where do we pave?
Each year a certain number of new roads are paved, selected based on factors such as housing density, existing conditions of roadway surfaces, and budgetary constraints. As an eligible community, our City does get limited annual financial assistance from a DOT administered State-Aid program (the Powell Bill), and these funds may only be used for roadway related maintenance or construction. BSL has an established Long Range Planning program, and certain roadways are targeted as potential paving candidates for future consideration.
For existing roadways, future pavement maintenance will be necessary in order to preserve and protect the roadways we have. Pavements age and typically lose their flexibility from several factors including UV degradation, temperature, and in some cases a lack of traffic activity. Several types of cracking patterns and broken pavements are observed, caused by structural failure, thermal contraction, or moisture trapped beneath the pavements in poor subbase materials (such as silt/clay soils).
A variety of methods exist to resurface pavements, seal cracks or patch sections. While it is important to prevent or minimize moisture intrusion, paving above improper candidates can cause cracks to reflect upwards through resurfacing and then the problem reoccurs. So we need to carefully evaluate any pavement sections with structural issues, and select the right course of action. In the future we intend to develop a Pavement Condition Index (PCI) program to assess and rate our roadway system.
These localized failures are often caused by inadequate base materials, drainage problems, or unraveling of the deteriorated pavement surface. In the past we have conducted large scale pothole repair programs periodically, with spot repairs made throughout the year. We are now considering the purchase of new equipment to implement a more consistent pothole repair program in the future.
Please continue to notify your Public Works Department when potholes are observed and become a nuisance. We appreciate this assistance and encourage you to bring these to our attention.
If you have any questions about this article, please contact the City Engineer at 910-363-0025