This paper describes recent research the aim of which was todevelop permanent deformation design transfer functions for unboundpavement layers from Heavy Vehicle Simulator (HVS) test data.Two types of data generated during an HVS test are used to developthe permanent deformation models on which the design transferfunctions are based. These are the in-depth deflection and permanentdeformation data obtained from the Multi-Depth Deflectometer (MDD)measurements taken at regular intervals during an HVS test. Testdata from a number of HVS tests, selected from the moderate andwet regions in South Africa, were used for the development ofthe permanent deformation models.

A multi-dimensional, conceptual model for permanent deformationwas developed and calibrated with HVS test data for pavement foundationand structural layers of different material qualities. These modelsprovide permanent deformation design transfer functions at differentexpected performance reliabilities for unbound pavement layersin South Africa.

The use of these design transfer functions is illustrated bya number of examples. The design approach allows each of the pavementstructural layers and the pavement foundation to contribute tothe total deformation or surface rut of the pavement structure.