Abstract:
Axle load distribution factors (ALDFs) are used as one of the primary traffic data inputs for
mechanistic-empirical (ME) pavement design methods for predicting the impact of varying
traffic loads on pavement performance with a higher degree of accuracy than empirical methods
that are solely based on equivalent single axle load (ESAL) concept. Ideally, to ensure
optimal pavement structural design, site-specific traffic load spectra data—generated from
weigh-in-motion (WIM) systems—should be used during the pavement design process.
However, because of the limited number of available permanent WIM stations (in Texas,
for example), it is not feasible to generate a statewide ALDFs database for each highway
or project from permanent WIM data. In this study, two possible alternative methods, namely,
the direct measurement using a portable WIM system and the cluster analysis technique, were
explored for generating site-specific ME-compatible traffic data for a highway test section,
namely, state highway (SH) 7 in Bryan District (Texas). The traffic data were then used for
estimating pavement performance using a ME pavement design software, namely, the
Texas Mechanistic-Empirical Thickness Design System (TxME). The TxME-predicted pavement
performance (e.g., rutting) using the portable WIM-generated traffic input parameters closely
matched with the actual field performance. Overall, the study findings indicated that the portable
WIM (with proper installation and calibration) constitutes an effective means for rapidly
collecting reliable site-specific ME-compatible traffic data.
