Pavement Structural Analysis of the Design Recommendations for ...

Pavement Structural Analysis August 2004
Report No. 15953-2/1 ARA-ERES Consultants
The truck traffic inputs for the new M-E Pavement Design Guide software, however, are
the actual truck volume distribution and axle load distributions. Table 1 shows the truck
traffic distribution that was used in this pavement design study. The Truck Traffic
Classification (TTC) group for this urban freeway was assumed to be 3. (3) Figures 2–4
show the axle load spectra for the single, tandem and tridem axles, respectively.
Table 1 Truck Traffic Volume Distribution for the Base Year, 2005.
Truck Type Normalized Volume Distribution, %
4 0.90
5 11.6
6 3.6
7 0.2
8 6.7
9 62.0
10 4.8
11 2.6
12 1.4
13 6.2
Using the default normalized truck volume and axle weight distributions determined from
an analysis of the Long Term Pavement Performance (LTPP) traffic data and the
AASHTO equivalency factors, the number of 18-kip (80-kN) ESALs were estimated for
the base year for this section of I-96. (3) Appendix A summarizes the computations for the
ESALs using the normalized axle load distributions that are expected for this urban
freeway. The number of ESALS was computed to be 4,411,425 in 2005 for both
directions, which is almost twice the value used in the 1993 AASHTO design procedure
(2,382,720 ESALs). The reason for this difference is not known, but indicates that the
global default distribution values embedded in the new M-E Pavement Design Guide
software may not be applicable to the truck traffic in Michigan, or at least should be
confirmed prior to full-scale use.
A lane distribution factor of 0.70 and a directional distribution of 0.56 were used to
compute the design-lane ESALs for 2005 – a value of 1,729,279. As noted above, the
ESALs determined from the volume and axle load normalized distributions
recommended for use in the new M-E Pavement Design Guide are greater than those
used in the design study completed by the Michigan DOT. The average number of 18kip
(80-kN) ESALS per truck application determined using the normalized distributions
was computed to be 1.259 (refer to Appendix A).
3