Please see the VERIFIED page for a couple of third-party reports verifying that PAVEXpress meets the design criteria of the AASHTO Guide for Design of Pavement Structures 1993 for flexible pavements and AASHTO Guide for Design of Pavement Structures 1998 Supplement for rigid pavements.  In addition, Washington State DOT also allows for use of PAVEXpress (WSDOT, p.11).