Several important issues concerning the effect of slab support on concrete pavement performance were studied in a National Cooperative Highway Research Program project, "Support Under Concrete Pavements" (NCHRP 1-30). The results were promising, however, the data that were available for analysis were limited. This study was conducted to further field-verify and develop the improved support guidelines proposed in NCHRP 1-30, using the Long-Term Pavement Performance (LTPP) database, in order to establish their practicality and appropriateness for use in concrete pavement design nationwide. This study was also conducted to further field-verify the proposed revised American Association of State Highway and Transportation Officials (AASHTO) performance model to the fullest extent possible using the design, materials, climate, traffic, and performance data available in the LTPP database for General Pavement Section 3 (GPS-3) (jointed plain concrete pavement), GPS-4 (jointed reinforced concrete pavement), and GPS-5 (continuously reinforced concrete pavement). Guidelines, revised on the basis of the results of this field verification study, are presented in the appendix in the form of a proposed addendum to the AASHTO Design Guide. The documentation of these field verification efforts using the LTPP database is provided in this report.