This paper describes a comprehensive investigation of strain tolerant type reflective crack relief interlayer systems through fundamental laboratory testing, computer aided design, and accelerated pavement testing. One of the widely used methods to control the reflection of cracks from underlying, cracked pavement into a new asphalt overlay involve the use of conventionally paved ‘interlayers’ that tolerate the very high tensile and shear strain that exists above cracks and joints in the underlying pavement. While these systems often slow down the rate of reflective cracking relative to untreated control sections in the field, when cracks do appear they are often offset from the location of the underlying discontinuity. A recently completed study sponsored by the National Science Foundation led to the development of a new fracture test (ASTM D7313-07b - the Disk-Shaped Compact Tension Test for Asphalt Concrete) and new techniques for finite element modeling of fracture in asphalt overlay systems. After successful validation of these tools on three field projects, it was decided to conduct further validation using the Advanced Transportation Loading System or ATLAS device and to experiment with new overlay configurations. A large experimental matrix was used to select promising interlayer materials and pavement layer and joint configuration details using finit e element analysis. A 500 ft(165 m) test pavement was constructed, instrumented, and tested in the cold of winter in 2008. This paper describes this comprehensive investigation, the new test sections developed, the types of distress observed under accelerated loading, and how the results were used to validate a new mechanistic analysis and design tool. Moreover, significant new insights towards the mechanisms and prevention of reflective cracking were obtained and have been summarized.