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To accomplish these objectives, several sequential tasks were performed. First, an extensive
literature search and review was undertaken to identify practices and experiences relating to
preservation of high-traffic-volume roads. Next, a comprehensive survey of preservation practices
was developed and distributed to all state highway agencies (SHAs) and selected other agencies to
obtain information on current preservation practices for hot-mix asphalt (HMA)- and portland
cement concrete (PCC)-surfaced pavements on high-traffic-volume roadways in rural and urban
settings. Information from the compiled literature and the questionnaire survey was summarized
and analyzed to identify the current state of the practice. Criteria were developed and applied to
focus on preservation approaches that are currently successfully implemented and on others that
have the potential to be successful but have not been regularly deployed. Detailed guidelines on
pavement preservation strategies for high-traffic-volume roadways were then developed using
the state of the practice and a comprehensive treatment selection framework and process.
Findings
Literature Review
Results of the literature review revealed several important items concerning pavement preserva-
tion practices in general and the use of preservation treatments on high-traffic-volume roads in
particular. First, there are a variety of conventional preservation treatments (and several less
widely used or new treatments) available for treating HMA- and PCC-surfaced roads, and these
treatments have unique features and capabilities that can (a) effectively prevent the development
of distresses or slow the development of existing distresses or (b) successfully restore the integrity
and functionality of a pavement or restore important surface characteristics (e.g., friction and
smoothness). The treatments entail the use of a variety of materials that can be placed in different
fashions and in different thicknesses and that require different times until opening to traffic.
Second, according to a 2004 National Cooperative Highway Research Program (NCHRP) survey
of SHAs (Peshkin and Hoerner 2005), pavement preservation is occurring as frequently, or even
more frequently in the case of rural roads, on higher-volume roadways than on lower-volume
roadways. The results from that survey suggested that the more important distinction is between
rural and urban roadways for any traffic volume.
Third, besides proper design and good quality of construction and materials, the performance
of preservation treatments--as measured by the extension in pavement service life imparted by
the treatment--is impacted by three key factors. These factors include the following:
· Condition of the existing pavement;
· Level of traffic under which the treatment must function; and
· Climatic conditions to which the treatment is exposed.
Fourth, climatic conditions can also have an effect on the constructability of some preservation
treatments. For example, some treatments, especially those based on asphalt emulsions, are best
applied under restricted temperature and humidity conditions. Climate can directly affect curing
time, which in turn impacts treatment feasibility and opening to traffic.
Finally, various international preservation practices were identified and reported. The proper
context for these strategies must be fully understood, because the way in which each country chooses
their preservation strategy depends on their standard road design, climate, traffic patterns, and
the political and economic organization of the country.
Survey Results
Results of the preservation survey revealed several key findings as well. First and foremost, SHAs
have different definitions regarding what constitutes a high-traffic-volume roadway. The criteria
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range from an average daily traffic (ADT) as low as 1,000 vehicles per day (vpd) to as high as
100,000 vpd, and several agencies have separate criteria for roads in rural settings and those in urban
settings (or, sometimes National Highway System [NHS] versus non-NHS roadways). To provide
a more consistent analysis of preservation treatment usage on roadways with different traffic levels,
an analysis of the survey responses regarding the high-traffic-volume criterion was performed.
Based on this analysis, high traffic volume was defined as an ADT of at least 5,000 and 10,000 vpd
for rural and urban roadways, respectively.
The most commonly used preservation treatments (greater than 50% of responding agencies)
according to these definitions of high-traffic-volume roadways were as follows:
· Rural HMA-surfaced roadways: Crack filling, crack sealing, thin HMA overlay, cold milling
and thin HMA overlay, and drainage preservation.
· Urban HMA-surfaced roadways: Crack filling, crack sealing, cold milling and thin HMA overlay,
and drainage preservation.
· Rural and urban PCC-surfaced roadways: Joint resealing, crack sealing, diamond grinding,
partial-depth repair, full-depth repair, dowel bar retrofitting (i.e., load transfer restoration),
and drainage preservation.
Treatments considered most inappropriate for use on high-traffic-volume facilities by survey
respondents included fog seal, scrub seal, slurry seal, chip seal, and ultra-thin whitetopping for
HMA-surfaced pavements and thin HMA overlay, ultra-thin bonded wearing course, and thin
PCC overlays for PCC-surfaced pavements.
The survey results indicated that the top three deficiencies addressed by preservation treatments
on HMA-surfaced pavements are light and moderate surface distress (i.e., various forms of
cracking), raveling, and friction loss. For PCC pavements, the top three pavement performance
issues addressed related to smoothness or ride quality and surface distress (i.e., spalling and various
forms of cracking), with some concern about noise issues.
Finally, the survey results showed that an overwhelming number of respondents reported
using overnight or single-shift closures for treatment application. Ultra-thin whitetopping on
HMA-surfaced pavements and thin PCC overlays on PCC pavements were the exceptions, as
they generally require longer closure times to allow for proper curing.
Guidelines Development
The results of the literature review and preservation survey provided valuable insights regarding
the following preservation treatment attributes.
Performance
· Effect of existing pavement condition (distress) and serviceability (smoothness) on treatment
performance;
· Effect of traffic volume on treatment performance;
· Effect of climate and environment on treatment performance; and
· Effect of treatment on pavement condition, serviceability, safety (friction, surface drainage
[splash/spray, cross slope]), and noise.
Constructability Issues
· Costs (agency and user);
· Complexity of construction;
· Availability of skilled and experienced or qualified contractors;
· Need for specialized equipment or materials;
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· Availability of quality materials;
· Climatic and environmental constraints;
· Traffic disruption;
· Traffic control constraints; and
· Restrictions on available time for lane closures to complete the work.
The information gleaned from the literature review and the survey results was combined with
additional information, concepts, and ideas to develop a comprehensive preservation treatment
selection framework and process. This process, shown in Figure ES.1, serves as the basis for the
guidelines developed in the study.
Current and Historical Pavement Performance Data
(from field surveys and testing and/or PMS database)
Overall condition indicator (e.g., PCI, PCR)
Individual distress types, severities, and extents
Smoothness (e.g., IRI, PI, PSI/PSR) Historical Design, Construction, and M&R Data
Surface and subsurface drainage characteristics
Safety characteristics Pavement type and cross-sectional design
Friction/texture (e.g., FN, MPD/MTD, IFI) Materials and as-built construction
Crashes Maintenance and rehabilitation (M&R) treatments
Pavementtire noise (i.e., materials, thicknesses)
Pavement
Preservation Major Develop Feasible
or Major Rehab Rehab Treatments
Rehab?
Pavement Preservation
Preliminary Set of Feasible Preservation Treatments
Assess Needs and Constraints of Project
Performance Needs Construction Constraints
Targeted/required performance Funding
Expected performance of treatments Time of year of construction
Existing pavement condition effects Geometrics (curves, intersections,
Traffic effects (functional class and/or pavement markings/striping)
traffic level) Work zone duration restrictions (i.e.,
Climate/environment effects facility downtime)
Construction quality risk effects (agency Traffic accommodation and safety
and contractor experience, materials Availability of qualified contractors and
quality) quality materials
Environmental considerations (e.g.,
emissions and air quality, recycling/
sustainability)
Final Set of Feasible Preservation Treatments
Selection of the Preferred Preservation Treatment
· Conduct cost-effectiveness analysis
Benefit-cost analysis
Life-cycle cost analysis (LCCA)
· Evaluate economic and noneconomic factors
Figure ES.1. Process of selecting the preferred preservation treatment
for high-traffic-volume roadways.
