The development of the Long-Term Pavement Performance (LTPP) Pavement Loading Guide (PLG) was initiated to improve the reliability of traffic load estimates for the LTPP sections that do not have measured axle load data. The PLG contains extensive traffic data obtained from the LTPP database that may constitute the best available source of traffic data at the national level, a user-friendly graphical interface, and guidelines intended to help the user with the development of axle load spectra. Because of these features, the PLG will also facilitate traffic projections for general pavement design and management purposes. The uncertainty associated with estimating annual axle load spectra was quantified by assuming that the measured data do not exist and must be estimated. The estimated data were obtained by using axle load spectra obtained at similar sites in the same jurisdiction and utilized prototype PLG software. The difference between the estimated and the measured traffic loads was quantified by expressing axle load spectra in terms of equivalent single-axle loads. The results show that reasonable traffic load estimates can be obtained by judiciously selecting replacement traffic data. Although the PLG can reduce uncertainty of traffic forecasts and facilitate traffic forecasting, surrogate data can never replace site-specific data.
Samenvatting