Summary: Caltrans has considerable experience with the use of rubber in dense graded asphalt concrete hot mix (DGAC). This experience began in 1978 and has continued to the present. The experience to date has indicated that the use of rubber in asphalt concrete can be cost-effective. On the early projects, Caltrans compared equal thickness of rubberized asphalt concrete (RAC) to conventional DGAC. The RAC has outperformed the conventional mixes on these projects, but the question of cost-effectiveness is difficult to answer since most of the projects are still in service. In 1983, a project was constructed using reduced thickness RAC (as compared to the design thickness for the conventional DGAC). This project, which is still being evaluated, has shown that thinner sections of RAC can outperform thicker sections of conventional DGAC. But the question that remains is what reduction in thickness can be made and still provide the desired service (design) life.