Rubberized Asphalt Studies in Other California Counties   Rubberized asphalt has been studied in other California counties outside of Sacramento. Orange County studied the effectiveness of rubberized asphalt as a noise mitigation measure in a report entitled Mixed Roadway Surface Noise, prepared by Mestre Greve Associates in February of 1992. The City of Thousand Oaks also conducted a study in 1992 entitled Asphalt Rubber Overlay Noise Study, prepared by Acoustical Analysis Associated, Inc. Both studies determined that rubberized asphalt successfully mitigated traffic noise.   The study conducted for the County of Orange looked at the difference in noise levels between four different pavement types: dense grade asphalt, rubber asphalt (gap graded), rubber asphalt (open graded), and open grade (with latex). The goal of this analysis was to eliminate the effect due to different traffic conditions at each segment of roadway thus resulting in a different noise level due specifically to the asphalt type. The study concluded that rubber asphalt-open graded was 3.9 dBA quieter than new dense grade asphalt.   The noise study conducted for the City of Thousand Oaks measured the reduction in traffic noise levels experienced due to resurfacing. The street conditions before resurfacing were poor and therefore, noise reduction due to the new paving was striking. Noise reduction on the six sites tested ranged from 3-7 dBA, depending on traffic and speed. When compared with the new standard asphalt, rubberized asphalt was found to be 2-5 dBA quieter.   National Rubberized Asphalt Studies   On a national scale, rubberized asphalt has been studied by many states as well as the federal government. Arizona has been the leader in the production and use of rubberized asphalt. In March 1990, Western Technologies Inc. performed a sound level survey to determine the noise levels produced during peak traffic flow on different types of pavement, including rubberized asphalt. In November of 1995 the Texas Department of Transportation conducted a study on the crumb rubber modifier used in rubberized asphalt as a successful method to reduce tire noise. Finally, the National Research Council conducted a study in 1997 entitled the Relationship between Pavement Surface Texture and Highway Traffic Noise.   Two studies were conducted in Arizona. One was prepared for the City of Phoenix and the other was prepared for the City of Tucson. The study in the City of Phoenix was compared standard chip seal asphalt laid in 1984, and rubberized asphalt that was laid in 1989. The study concluded that there was an approximate 10 dBA reduction in noise with the rubberized asphalt compared with the chip seal asphalt.   The study prepared for the City of Tucson compared asphalt rubber concrete pavement and standard concrete pavement. The study showed that the asphalt rubber concrete was 6.7 dBA quieter than the concrete pavement.   In 1995, the Texas Transportation Institute conducted a study to identify potential problems with the current rubberized asphalt mix design, develop recommendations on those problems, develop recycling guidelines, and evaluate alternatives. Researchers monitored CRM mixtures paved in 1992 and 1993 in San Antonio, Texas. The results of the these tests concluded that rubberized asphalt performed well in construction practices, and that the rubberized asphalt mixes gives a higher durability with better stability than dense-grade mixes.   The National Research Council conducted a study showing the effect of different surface types on noise levels. The Council studied many types of roadway surfaces and determined that open graded asphalt showed the greatest potential for noise reduction when compared to dense graded asphalt. The study examined research done by Kansas, that studied the effects of rubberized asphalt. The results in Kansas showed that the open graded asphalt always showed a decrease in noise level. In contrast, when the asphalt rubber pavement was compared to the asphalt surface, there were both reductions and increases in noise level. Thus, the results of this Kansas study did not show a clear noise reduction trend with rubberized asphalt. However, the study done by the National Research Council did not examine any other research than the Kansas study.   Global Studies   Rubberized asphalt is a process that is not only of interest in the United States but also globally. In 1995, the Canadian Technical Asphalt Association performed a study for British Columbia on rubberized asphalt. Their study entitled, The Full Scale Evaluation of Rubberized Asphalt Concrete in British Columbia, was a response to the need for improvement of binders in the road building industry. In a paper done by Netherlands researchers, entitled Open Grade Rubberized Asphalt for Traffic Noise Reduction in Urban Areas, research was conducted to analyze the development of rubberized asphalt as a mitigation measure. Other studies have been done in Great Britain, West Germany, Belgium, and other European Countries.   The study conducted in British Colombia compared conventional pavement binders to Rubberized Asphalt (Rub-Arb [TM]) in various locations throughout British Columbia over a period of five years. This study concluded that within the laboratory, the asphalt rubber binder showed improved properties at extreme temperatures compared to convention asphalt. This study also concluded, that modified asphalt rubber binders can be manufactured for a wide range of climate conditions and requirement, it is more flexible at low and sub-zero temperatures, and that the thickness of the asphalt rubber concrete overlay can be reduced from the traditional 50mm overlay down to 38mm of modified asphalt rubber concrete.   In Dordrecht, Belgium a test was conducted using open graded rubberized asphalt in order to study the effectiveness of rubberized asphalt on noise. In this study the researchers concluded that it is possible to design an asphalt mix to reduce traffic noise in urban situations where the traffic noise is dominant. The study found, that a noise reduction can be achieved of between 2.1 and 3.2 dBA at the speeds of around 50 km/h.   Additional studies have been conducted in other European countries. The Societe des Autoroutes du Nord et de l'Est de la France, Paris conducted a study that showed a noise reduction level of 2-3 dBA with rubberized asphalt along the Seine River. In a paper presented at the 1988 Asphalt-Rubber Conference in Graz, Austria, Helmut Prager, Engineer of Austrian Highways and Bridges showed how the rubber overlay provides better noise reduction. Finally, in Bonn, Germany a study showed that using rubberized asphalt as a sound mitigation measure is more cost effective than using sound barriers. Most of these studies concluded that rubberized asphalt could reduce noise by 2-3 dBA with few technical problems.   Finally, The European Commission Green Paper, published in the June 1997 edition of Noise/News International, cites the following on Page 87:   "Low-noise porous road surfaces have been the subject of much research. These porous road surfaces reduce both the generation and propagation of noise by several mechanisms - which can be related to the open structure of the surface layer. Results have shown that the emission noise levels can be reduced from levels generated on equivalent non-porous road surfaces by between 3-5 dB(A) on average; by optimizing the surface design, larger noise reductions are feasible. At present, the cost of porous asphalt surfacing is higher than conventional surfaces (for resurfacing, but for new roads, the cost is minimal), but may drop as contractors gain experience with porous surfaces. The material is also less durable. However, improvements are being made to durability and, in many countries, these materials are already being used as part of normal road construction in noise-sensitive areas."   Table of Contents | Executive Summary | Introduction | History of Noise Reducing Pavement | The Process of Producing Rubberized Asphalt | Current Uses of Rubberized Asphalt | Tables | Studies of Rubberized Asphalt Outside of Sacramento County | Sacramento County Rubberized Asphalt Noise Studies | Conclusions of the Studies Conducted in Sacramento County | Appendix A - Acoustical Terminology | Appendix B - Noise Standards Commonly Applied to Projects in Sacramento County