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Improved characterization of truck traffic volumes and axle loads for mechanistic-empirical pavement design.
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2012-12-01
[PDF-10.89 MB]
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Edition:Final report.
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Abstract:The recently developed mechanistic-empirical pavement design guide (MEPDG) requires a multitude of traffic
inputs to be defined for the design of pavement structures, including the initial two-way annual average daily truck
traffic (AADTT), directional and lane distribution factors, vehicle class distribution, monthly adjustment factors,
hourly truck distribution factors, traffic growth rate, axle load spectra by truck class (Class 4 to Class 13) and axle type
(single, tandem, tridem, and quad), and number of axles per truck. Since it is not always practical to obtain sitespecific
traffic data, the MEPDG assimilates a hierarchal level concept that allows pavements to be designed using
statewide averages and MEPDG default values without compromising the accuracy of the pavement design. In this
study, a Visual Basic for Application (VBA) code was developed to analyze continuous traffic monitoring data and
generate site-specific and statewide traffic inputs. The traffic monitoring data was collected by 143 permanent traffic
monitoring sites (93 automated vehicle classifier (AVC) and 50 weigh-in-motion (WIM) sites) distributed throughout
the State of Ohio from 2006 to 2011. The sensitivity of the MEPDG to the various traffic inputs was evaluated using
two baseline pavement designs, one for a new flexible pavement and one for a new rigid pavement. Key performance
parameters for the flexible pavement included longitudinal (top-down) fatigue cracking, alligator (bottom-up) fatigue
cracking, transverse (low-temperature) cracking, rutting, and smoothness (expressed using IRI), while key
performance parameters for the rigid pavement included transverse cracking (% slabs cracked), joint faulting, and
smoothness. The sensitivity analysis results revealed that flexible pavements are moderately sensitive to AADTT,
growth rate, vehicle class distribution, and axle load spectra; and not sensitive to hourly distribution factors, monthly
adjustment factors, and number of axles per truck. Furthermore, it was found that rigid pavements are moderately
sensitive to AADTT, growth rate, hourly distribution factors, vehicle class distribution, and axle load spectra; and not
sensitive to monthly adjustment factors and number of axles per truck. Therefore, it is recommended to estimate the
AADTT and the vehicle class distribution from site-specific short-term or continuous counts and obtain the truck
growth rate from ODOT Modeling and Forecasting Section (Certified Traffic). As for the other traffic inputs,
statewide averages can be used for the hourly distribution factors, axle load spectra, and number of axles per truck; and
MEPDG defaults can be used for the monthly adjustment factors.
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