Quieter Pavements. The transportation
agencies responsible for preserving and improving modern highway systems have historically
made public safety their first concern when designing pavement surfaces. In practice this
meant focusing on roadway smoothness and friction, both of which keenly influence
safety. Over the past decade, however, the public has grown more concerned about the noise
generated by highways, and this has spurred agencies to investigate ways to mitigate that
sound.
A common noise-abatement strategy traditionally selected by agencies has been the
construction of sound walls, but in recent years departments have also sought to expand their
tools and strategies for minimizing the effects of highway noise on the general public. One
strategy currently under development is use of “quieter pavements.”
Quieter pavements have surface textures that minimize the noise generated from
their interaction with car and truck tires. (While tire/pavement interaction is not the only
source of highway noise generation, it is a significant contributor, particularly with traffic
moving at high speeds.)
In 2004, Caltrans requested that the UCPRC initiate a study into the sound
properties of commonly used pavement surfaces as well as new types. The study’s primary goal
is to monitor the sound properties of asphalt and concrete pavement surfaces over time on
more than 100 sections around the state—by measuring on-board sound intensity (OBSI) at the
tire/pavement interface. Also being measured are changes in the properties that determine
tire/pavement noise, such as the deterioration of the pavement surface, structural damage
such as cracks, and the clogging of permeable surfaces. These results, and findings from
other studies by Caltrans, consultants, industry, and other states and countries, are
being used to help determine the best practices for pavement surfaces to minimize noise.
The UC Pavement Research Center OBSI test vehicle.
In addition to monitoring of highway test sections, an extensive laboratory
study was also performed to develop new open-graded asphalt mixes that have the potential to
provide improved noise reduction with greater durability. Starting in January 2012, some of
these mixes will undergo accelerated pavement testing with the Heavy Vehicle Simulator (HVS) to
evaluate their durability compared to current mixes. Pilot projects will follow.
New types of concrete pavement surfaces developed by industry and other
universities are also being evaluated on highway test sections in California. For example,
transverse tining has been used in many states—although not in California—to provide a
safe, skid-resistant driving surface on concrete pavements, but an unintended consequence of
using this texture is high tire/pavement noise. While California has used a variety of
textures that are generally quieter than transverse tining—such as longitudinal tining
and conventional grinding—to provide skid resistance, new texturing techniques have been
developed from recent research at Purdue University. Collectively called the Next Generation
Concrete Surface (NGCS), these pavement surfaces are intended to provide good skid resistance
with less noise generated by tire/pavement interaction (a pavement surface ground with the
NGCS above a typical concrete grinding pattern is shown on the right, above). The UCPRC is working with
Caltrans and industry to measure the potential benefits of this new surfacing on several
pilot projects in the San Diego and greater Sacramento areas. The performance of the pavement
surface is being characterized by OBSI testing (the specially-equipped vehicle is
shown on the right, below), International Roughness Index (IRI) measurement, skid resistance tests,
friction tests, and surface texture scans. Tests will be conducted annually, in conjunction
with the ongoing noise study, to evaluate the long-term performance of these new concrete
surfaces.
Important Note for Caltrans Users: Prior
to scheduling pavement preservation (preventive maintenance or CAPM) or roadway
rehabilitation work on flexible pavement highway sections, the District Materials
Engineer and/or the Project Manager should review
this spreadsheet to
ensure that the proposed project does not include sections active in
the “Quieter Pavement Research” (QPR) testing program. If the proposed
project is within a QPR test section, please
contact Linus Motumah of the
Caltrans Office of Pavement Design before scheduling the work.
To view maps that show where the sections are located, click the following
link: http://maps.google.com/maps?q=http://www.ucprc.ucdavis.edu/qpsectionsmap.kmz
(or copy-and-paste it into a new browser window for a slightly larger view).
For more information,
contact John Harvey of the UCPRC or
Linus Motumah.