There are lots of things that we bring someplace for a regular checkup. You might take your kid to the dentist, your car to the mechanic, or your dog to the vet. Pavements should be checked regularly as well, as part of the practice we call pavement management. In this edition of the RoadReady newsletter, we’ll introduce the concept of pavement remaining service interval (RSI), how it differs from existing terminology, and some of the implications for pavement management.
Remaining Service Interval
The concept of “remaining service interval” for a pavement can be explained as the time remaining until a defined construction treatment. Remaining service interval, or RSI, is similar to the existing concept of remaining service life (RSL), which is often used to express the time remaining until the condition of the pavement reaches a level unacceptable for use. However, the RSL terminology has been used and interpreted in different ways, and the Federal Highway Administration (FHWA) has endorsed a shift to using terminology based around the RSI concept instead.
Agencies need to predict the remaining service period of a pavement in order to forecast, budget, and plan for future repairs. The RSL concept provided a simple way to do that, often based on the design of the pavement. In the absence of other information, the design period of the pavement might be treated as equivalent to the remaining life. For pavement management purposes, however, the as-designed pavement is less significant than the performance and properties of the as-constructed pavement. A framework built around RSI instead of RSL could help ensure that these aspects are properly accounted for in evaluating the pavement.
Another reason the FHWA supports a transition to the RSI concept is that remaining service “life” may lead to confusion in a variety of ways. One challenge is the ambiguity of defining service life, since the assumptions and estimates made during design are not necessarily carried forward into pavement management activities. In addition, even when part of the system fails and needs repair, it seems strange to measure system life based on something that can be corrected. Finally, the FHWA is concerned that RSL terminology may unintentionally promote “worst-first” approaches to pavement management that lead to increased costs and reduced efficiency.
Intervals to Multiple Construction Events
One of the advantages of the RSI framework is that it allows agencies to simultaneously account for multiple events over the timeline that a pavement is in service. For example, a pavement might be expected to reach the threshold for a maintenance treatment like a slurry seal in a relatively short timeframe, such as 2 years; a rehabilitation treatment such as a thin asphalt overlay might be anticipated after a 6-year interval; and the pavement might be scheduled for full reconstruction in 15 years. Each of these time periods constitutes the RSI for the pavement as to that category of treatment.
Because RSI acknowledges different types of construction events in the life of a pavement, this should help integrate the RSI approach with best practices in pavement management. Agency policy decisions as well as pavement management systems increasingly factor in the need to plan for different treatments at different pavement condition thresholds. Each of these can be expressed and analyzed in terms of RSI. This provides more flexibility than having an approach focused primarily on one terminal event to mark the end of a cycle.
Thresholds and Triggers
Like other aspects of pavement management, the RSI framework depends on periodic assessments of pavement condition to determine when treatments are needed. Having a measurable way of identifying pavement condition makes it possible to set condition thresholds for different categories of treatments and to create rules that trigger appropriate construction events. When indicated by the condition of the pavement, a corrective treatment can be applied. The pavement RSI for a particular treatment is effectively a prediction of the time until the pavement condition will trigger the need to apply that treatment.
In conjunction with pavement management software programs, the RSI framework can build on performance curves that predict future pavement condition based on analysis of observed performance. The interval until the next treatment can be calculated on the basis of the performance curve. Additional data analysis makes it possible to assess how treatments perform relative to each other as well as the performance curve model. This allows an agency to fine-tune service intervals, adjust treatment selection, and improve its overall pavement management strategy.
Keeping Roads Alive
We sometimes talk about roads as if they feel alive. That may be on account of the driving experience, the scenery they bring us to, or some other special characteristic. Metaphorically, roads may live, but it doesn’t mean that service life must reach an end. Rather, the idea is to keep the road as healthy as possible until the next time work is needed, and then to apply a treatment that helps the road live even longer. Reformulating pavement management terminology to use a pavement’s remaining service interval (RSI) rather than focusing on service “life” could help reflect that understanding.
Federal Highway Administration, Techbrief: Pavement Remaining Service Interval: http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/13039/13039.pdf
Federal Highway Administration, Pavement Remaining Service Interval Implementation Guidelines: http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/13050/13050.pdf