California Applications and Experiences Using the OBSI Method

In 2001 Caltrans began experimenting with a little known acoustic measurement process originally invented by General Motors to quantify tire/pavement noise during automotive development. Caltrans adapted the process to quantify pavement/tire noise in support of their evolving Quieter Pavement Research Program. General Motors had used this sound intensity based process to quantify the acoustics of many different tires on a single pavement on a closed test-track. Caltrans would adapt the process to use a single test tire on many different pavements on an open roadway, ‘floating’ in a 60 mph traffic stream with other vehicles. This relatively inexpensive, fast, and portable measurement process is now being adopted as a national standard specification by both AASHTO (and ASTM) and is referred to as the On–Board–Sound–Intensity (OBSI) Methodology. The California developed process is currently being used by several other State DOTs and pavement research organizations and has proven to be an important new tool for assessing pavement noise impacts on community noise levels. OBSI provides acoustic data for both research and routine work. OBSI is particularly useful for providing data that can be used to select quieter pavement strategies which can yield immediate benefits in lowering roadside noise levels. This paper presents practical applications for the OBSI Method and of some findings in Caltrans’ Quiet Pavement Research Program.