The current Climate (CLM) module of the Long-Term Pavement Performance (LTPP) database began as the Environment (ENV) module in 1992, with major revisions and enhancements performed in 1998. Since 1998, pavement technology and the use of climatic data have evolved (with adoption of the Integrated Climatic Model in the Mechanistic-Empirical Pavement Design Guide (MEPDG), for example), and there is a need for a reassessment of climatic data in general, and the sufficiency of LTPP climatic data collection specifically. During the last climate data update performed by the LTPP program in 2008, there has become a need to create a time series-based operating weather stations (OWS) selection strategy. The reason for this is that over the 20 years of the LTPP program, new weather stations have been added, others are no longer operational, and the locations of exiting weather stations have changed, although their station identification remained the same. There is a need to develop a methodology to treat estimates of location-specific climate data from surrounding weather stations whose locations and characteristics change over time. There is also a need to develop an estimate of variability or uncertainty in climate estimates derived from the averaging process of nearby weather stations. The National Cooperative Highway Research Program (NCHRP) 1-34D study on pavement drainage found a better correlation between the Thornthwaite Moisture Index (TMI), which is a climate-soil moisture holding potential interaction parameter, than traditional precipitation-based climate indices. The LTPP Automated Weather Station monitoring measurements have been terminated; however, no assessment of the value of the solar radiation data collected by this study have ever been made against other data sources, nor has the use of solar radiation data from other data sources for more widespread inclusion in the LTPP program been assessed. It is not yet known how, if any, issues associated with global warming caused by increases in solar output, a decrease in the ability of the earth's atmosphere to reflect this radiation, or a combination of these effects, will affect the service life of pavement materials being used today.
The key project objective is to develop guidance for implementing climatic data for use in Mechanistic-Empirical Pavement Design Guide (MEPDG) calibration and other pavement analyses.