The new Mechanistic-Empirical (M-E) Pavement Design Guide and accompanying
software are now available in a review version for testing and evaluation
by highway agencies and others worldwide. Developed under National
Cooperative Highway Research Program (NCHRP) Project 1-37A, the Guide
provides a uniform basis for the design of flexible, rigid, and composite
pavements, using mechanistic-empirical approaches that more realistically
characterize inservice pavements and improve the reliability of designs.
"The new Guide presents nationally calibrated distress models that
are available for States to use for the design and analysis of their
pavements," says Katherine Petros of the Federal Highway Administration
(FHWA).
The proposed Design Guide was developed to replace the 1993 American
Association of State Highway and Transportation Officials (AASHTO)
Guide for Design of Pavement Structures, which was based on empirical
equations derived from the road test conducted by the then American
Association of State Highway Officials (AASHO) between 1958 and 1960.
The road test used a limited number of pavement sections at one location,
with traffic levels far below those of today.
One of the primary benefits of the new Guide is that it uses M-E
numerical models to analyze input data for traffic, climate, materials,
and proposed structure and to estimate damage accumulation over the
pavement's service life. "The models are based on data from across
the United States, with far wider potential application than those
previously used," says Ed Harrigan of NCHRP. Analysis can be done
for designs for new, reconstructed, and rehabilitated pavements. Performance
predictions are made in terms of distress and smoothness, with the
predicted distresses for flexible pavement designs being longitudinal
cracking, alligator cracking, transverse cracking, and rutting. For
rigid pavement designs, the predicted distresses are faulting, cracking,
and continuously reinforced concrete pavement punch-outs. The design
performance values can be compared to threshold values or to alternate
designs.
The Guide also allows for consideration of special loadings, with
multiple tires or axles, and provides a means for evaluating design
variability and reliability. And it can be used to analyze the condition
of existing pavements and pinpoint deficiencies in past designs.
Over the next few years, the AASHTO Joint Task Force on Pavements
will continue evaluating the proposed Guide. FHWA will also work with
the Joint Task Force to introduce the Guide to States and others through
workshops, training courses, and conferences. FHWA has established
a Design Guide Implementation Team (DGIT) to coordinate implementation
activities. The team sponsored a series of workshops introducing the
Guide this year (see sidebar), and plans to hold additional workshops
in 2005. For more information on the DGIT, visit www.fhwa.dot.gov/pavement/dgit.htm,
or contact one of the team members listed in the sidebar on this page.
The M-E Pavement Design Guide and software are available online at
www.trb.org/mepdg.
Comments on the Guide and software and suggestions for their further
improvement can be sent to Ed Harrigan at NCHRP, fax: 202-334-2006
(email: pavement-guide@nas.edu).
The DGIT has also established a Design Guide Community of Practice
Web site, which provides a central forum for user dialogue. To participate
in the Community of Practice, visit knowledge.fhwa.dot.gov/cops/hcx.nsf/home
and then choose the NCHRP 1-37A Pavement Design Guide Group.
FHWA Design Guide Implementation Team
Katherine Petros, 202-493-3154
Leslie Myers, 202-366-1198
Monte Symons, 404-562-4782
Sam Tyson, 202-366-1326
Any of the team members can also be contacted at: DGIT@fhwa.dot.gov.
Design Guide Workshops
FHWA's Design Guide Implementation Team will hold workshops on October
20 in Phoenix, Arizona, and on October 26 in Thornburg, Virginia.
For more information or to register, visit www.fhwa.dot.gov/pavement/dgitfly2.htm
or contact one of the DGIT team members listed on this page. In early
2005, the DGIT will also be holding a series of workshops on the materials
inputs for the Design Guide. These workshops will be aimed at bringing
highway agency pavement designers and materials engineers together
to discuss the materials-related input needs for those using the Design
Guide. Focus will provide additional information on the 2005 workshops
once they have been scheduled.
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| The new Pavement Design Guide provides a uniform basis
for the design of flexible, rigid, and composite pavements. |
