Some distressed roads need to be fixed right away, some don’t. If you are in charge of a municipality’s pavement management decisions then you have probably been faced with the difficult decision about how to optimize the spending of a limited budget. To navigate those situations with expertise you must be aware of the deferment cost.
In pavement management, road segments are assigned a score depending on their overall quality; this is known as a PCI, or Pavement Condition Index. Depending on the PCI score of a street, pavement management software will recommend a suggested rehab treatment and factor in the average cost. There are a variety of rehab categories to be aware of, all varying in cost depending on the functional classification of the roads in question.
Streets with a low PCI score of 0-25 are generally considered to be in very poor condition, where as a street with an 85-100 PCI will be considered excellent. A very poor street will require reconstruction to return it to full service, while an excellent street does not yet require any rehabilitation effort. Streets that score slightly above poor, usually in the 40-50 (marginal) range are generally the streets that need the most urgent attention. The reason for this is that these streets usually present the last opportunity for surface-based repairs. In general, the service life of these streets is such that if deferred for too long, they will require costly reconstruction. Streets rated as marginal are typically selected first for rehabilitation as they provide the greatest cost/benefit to the City by providing the greatest increase in service life per rehabilitation dollar spent.
Deterioration and Performance Curves
A successful pavement management program develops a confidently accurate performance model of a roadway, and then identifies the optimal timing and rehabilitation strategy for its needs. The benefits of this exercise are long term cost savings and an increase in pavement quality over time. The key is to develop policies and practices that delay the inevitable total reconstruction for as long as practical yet still remaining within the target zone for cost effective rehabilitation. That is, as each roadway approaches the steepest part of its deterioration curve, apply a remedy that extends the pavement life, at a minimum cost, thereby avoiding costly heavy overlays and reconstruction.
In this graph the different color lines represent various conditions that may affect the overall deterioration rate of a road. This can include heavy traffic growth, poor foundation materials, intense weather conditions and more.
A pavement information management software can track the deterioration of your entire network and recommend the proper rehabilitation activities as a road approaches its “need year”. Without a fully implemented pavement information management system, the process of identifying and tracking the need year of every segment of road in an entire pavement network is borderline impossible. The need year refers to the last possible year where a particular rehab treatment will be effective. If a street in its need year is deferred, a more costly treatment will be required to return the street to full service.
Avoid the Management Pothole
A trap that municipalities often fall into revolves around the worst-first rehab philosophy. The idea behind this management strategy is very straight forward; repair the most distressed streets first. This is a poor management strategy for a number of reasons. A cost comparison of rehabilitation techniques makes this concept much clearer: (Unit rates may vary slightly by location)
In the chart above, notice the increase in cost between Rehab Code 56 and Rehab Code 70, and again between 26 and 30. In this particular example the cost doubles from surface based overlays to base reconstructions, and quadruples from surface treatments to overlays. For the cost of a single mile of reconstruction, a municipality could instead extend the life of 5 miles of other roads in need of thick overlays. Keep in mind that the segments in need of Thick Overlays (Rehab 56) will soon become full reconstruction candidates, increasing their rehab cost 2 fold (500K becomes 1M). A pavement segment that requires reconstruction will not increase in cost through deferral; it will simply remain a reconstruction candidate until it receives proper treatment. Proper rehab planning could be the difference between $1,000,000 for a single mile of reconstruction or $100,000 for a single mile of surface based repairs.
Pavement managers are constantly wrestling with lengthy lists of rehab needs. In order to precisely manage a limited budget while dealing with these needs, it is important to adopt pavement management software that can organize the network streets. By actively rehabilitating roads in their need year and utilizing proper rehab deferment techniques, pavement managers can optimize taxpayer budgets and provide better services to the community.
Want to learn more about setting up a pavement management program in your city? Check out "Designing and Implementing a Pavement Management System" - An IMS Whitepaper