HD9 - The Virginia Quiet Pavement Implementation Program Under Section 33.1-223.2:21 of the Code of Virginia - Second Interim Report - June 2013
Chapter 790 of the 2011 Virginia Acts of Assembly (Code of Virginia § 33.1-223.2:21; see Appendix A) provides, in part:
"The [Virginia Department of Transportation] shall expedite the development of quiet pavement technology such that applicable contract solicitations for paving shall include specifications for quiet pavement technology and other sound mitigation alternatives in any case in which sound mitigation is a consideration. To that end, the Department shall construct demonstration projects sufficient in number and scope to assess applicable technologies. The assessment shall include evaluation of the functionality and public safety of these technologies in Virginia's climate and shall be evaluated over two full winters. The Department shall provide an interim report to the Governor and the General Assembly by June 30, 2012, and a final report by June 30, 2013. The report shall include results of demonstration projects in Virginia, results of the use of quiet pavement in other states, a plan for routine implementation of quiet pavement, and any safety, cost, or performance issues that have been identified by the demonstration projects."
Chapter 120 of the 2013 Acts of Assembly (see Appendix B) amended the foregoing language to provide for a second interim report and a 2-year extension of the deadline for the final report. This document is the second interim report. It provides the status of the lower noise pavement technologies that were demonstrated during the 2011 construction season. It also describes two additional trials that were constructed in 2012 and discusses two sections of quiet asphalt materials that were installed at the accelerated pavement testing facility at the National Center for Asphalt Technology (NCAT) at Auburn University in Auburn, Alabama.
First Interim Report: June 2012
The first interim report was delivered to the General Assembly in June 2012. It described the selection of lower-noise pavement technologies (i.e., “quiet” pavement [QP]); the development and construction of demonstration projects for the first season (2011) of the project; and the evaluation tools and analysis that were used to compare the performance of the alternative technologies. The selected QP technologies included three asphalt surface materials and two mechanically applied finishes for concrete pavement. The three asphalt surface materials included two open-graded asphalt concrete mixtures (with different gradations) that used a polymer-modified binder. The third had a similar aggregate gradation but had a rubber-modified binder. The two concrete technologies were conventional diamond grinding (CDG) and the Next Generation Concrete Surface (NGCS), which consists of diamond grinding followed by a “flush-grind” operation and then a final longitudinal grooving step.
Summer and fall 2012 activities included installation of two trial sections of quiet asphalt materials at the NCAT Pavement Test Track (www.pavetrack.com). The raw materials from the most promising 2011 demonstration technologies were sent to NCAT, blended with standard materials to produce “Virginia” QP technologies, and placed on the test track. Components of these technologies were also brought together to create two more demonstration projects in Virginia, one in the Northern Virginia District and the other in the Culpeper District.
Purpose and Scope
This report is the second in a series of documents that chronicle the selection of lower-noise pavement technologies; the development and construction of demonstration projects; and the evaluation tools and analysis being used to compare performance of the alternative technologies. This second interim report is focused on the additional QP sections that were constructed in 2012 and also provides the status regarding the performance of the 2011 series of demonstration projects.
Selection of Technologies for 2012 Demonstration
Early feedback from the 2011 QP demonstrations helped researchers identify candidate technologies for additional pilot projects for the 2012 construction season. These preliminary findings were also instrumental in the selection of the technologies being subjected to accelerated trafficking at NCAT. Since none of the materials and treatments from 2011 had premature material failures or essential functional problems (such as low winter skid resistance), tire-pavement noise performance served as the key discriminator for determining which technologies to pursue.
Evaluation of the original (2011) demonstration projects, as well as the assessment of the new 2012 projects, continues to focus on tire-pavement noise performance. Secondary testing to assess comfort and safety characteristics is also part of the regular regimen of tests. A complete description of each test method is included in the first interim report, but the current report does include a brief overview of the On-Board Sound Intensity (OBSI) and the GripTester continuous friction test methods for measuring noise and skid resistance, respectively.
Preliminary Findings and Discussion
When comparing noise levels of QP technologies, it is important to understand that decibels (dB) are logarithmic units and cannot be added by normal arithmetic means. Although precision instruments can measure small changes in sound level, the human ear requires about 3 dB of difference for the change to be “noticeable.” A 5 dB change is considered “readily noticeable” to most people, and a 10 dB difference is equivalent to a doubling (or halving) of the sound level.
As of spring 2013, the difference in measured tire-pavement noise between the control (typical) surfaces and the most successful (lowest noise) quiet asphalt technology was readily noticeable (?5 dB). The lowest noise experimental concrete surface also maintained a readily noticeable (?5 dB) advantage over the standard concrete pavement surface. The noise of the quiet concrete surfaces appears to have slightly decreased since the surfaces were first installed, whereas that of the quiet asphalt materials has slightly increased. In neither case is the difference perceptible by human hearing. All of the surfaces continue to have good resistance to skidding. There have been no reports of unique safety concerns associated with winter weather, and local maintenance crews are learning to be proactive (early and more frequent treatment) with regard to freezing precipitation on the porous surfaces.
Costs and Quantities
Table ES1 (shown on page xi of the report) shows the average initial cost and total quantity for each QP technology evaluated since the beginning of the program. Since the asphalt technologies are placed at varying thicknesses and the concrete technologies simply “refinish” the existing surface, the cost figures are normalized to an average per-surface-area cost (i.e., per square yard). Bear in mind that these are initial costs only and do not reflect any investment that is necessary to prepare a platform for the QP surface. A responsible cost comparison between any technologies should be made on a cost-per-year basis. These annualized cost figures will depend on reliable estimates of service life. Those estimates are a key objective of the remaining program of research.
Researchers will continue to monitor the functional (e.g., noise, friction, ride quality) performance of the installed technologies through at least 2015. Fall 2013 performance testing is also expected to include more in-depth structural tests of the material and overall pavement systems.
Virginia is one of many partner states that sponsored the 2012 rebuild of the NCAT Pavement Test Track. Virginia will not only receive regular performance feedback on the Virginia QP sections but will also have ready access to early findings from similar experiments at the test track sponsored by other states. The sections from other states are designed to provide answers regarding purported material and bond-related failures. To the extent that any of these issues might relate to Virginia’s evaluation program, this research will be ready to adopt suitable solutions quickly.
Another element of the evaluation program will be a trial vacuum-sweeping regimen to determine if it extends the functional advantages of porous surfaces. The bi-directional nature of the 2011/2012 projects will make it possible to perform the vacuum maintenance in one direction only and use the other direction as a control to determine whether the maintenance is effective.
Finally, researchers will continue to monitor federal legislative and regulatory developments in the area of QP technology. In particular, researchers will focus on monitoring the extent to which federal law and regulations may begin to consider QP technology more favorably as a viable alternative to noise walls or sound barriers as a sound mitigation measure.