Based upon the outstanding performance of this project as well as many others, ADOT routinely uses AR gap graded and open graded mixes throughout the state. Over 3,333km (2,000 miles) of AR projects have been built since 1990. Figure 5 is a map showing those ADOT system miles paved with AR. In addition the performance of all AR projects has been tracked through the ADOT PMS, Figure 6 shows the percent cracking for those overlay projects built with and without AR since 1988 (6). As shown the percent cracking is much less over time than for conventional overlays without AR. In addition Figure 7 shows less routine maintenance for AR projects than for conventional overlays. It should also be noted that the average thickness of the AR projects is 42.5mm (1.7 inches) and for conventional mixes it is 137.5mm (5.5 inches). Thus even though AR mixes cost about twice as much per ton, they are generally placed half as thick and crack at a rate less than one fourth than that of conventional mix. The overall AR performance seems to be in agreement with findings in 1977 (7) that AR in cold weather can withstand about five times the strain before rupture than can asphalt.

The Arizona Department of Transportation in cooperation with The Federal Highway Administration and the Strategic Highway Research Program have designed and constructed an extremely valuable research project. Field performance in nine years of service is providing experience indicating the effectiveness of a thin flexible overlay and wearing course composed of asphalt rubber. Results of this work are being incorporated into paving projects, throughout the state. Continued field performance measurements provide the data necessary to develop rational cost effective designs.