In 1990, the Arizona Department of Transportation designed and constructed a large scale Asphalt Rubber (AR) test project in Flagstaff, Arizona on the very heavily traffiked Interstate 40. The purpose of the test project was to determine whether a relatively thin overlay with AR could reduce reflective cracking. Asphalt Rubber is a mixture of 80% hot paving grade asphalt and 20% ground tire rubber. This mixture is also commonly referred to as the asphalt rubber wet process or McDonald process. The overlay project was built on top of a very badly cracked concrete pavement, which was in need of reconstruction. The asphalt rubber overlay has performed beyond the original expectation. After nine years of service the overlay is still virtually crack free, with good ride, virtually no rutting or maintenance and good skid resistance. The benefits of using asphalt rubber on this project represents about $18 million dollars in construction savings and four years less construction time. Strategic Highway Research Program SPS-6 test sections built in conjunction with the project further illustrate the very good performance of the asphalt rubber. Results of this project have led to widespread use of asphalt rubber hot mixes throughout Arizona. Based upon this work over 3,333km (2,000 miles) of successfully performing asphalt rubber pavements have built since 1990.