Freeway Sound: Pervasive, Possibly Harmful If Unmanaged

Saturday, July 2, 2011

Noise is one of the most pervasive pollutants in our environment, and, in Rockridge as in many communities, much of it originates from surface transportation: cars, trucks, trains, and motorcycles. This noise can be difficult or expensive to block in older homes, and nearly impossible to block in yards outside the homes.

Noise is unwanted sound and can be harmful at certain levels. The most obvious problems involve hearing loss from exposure to loud noise. The World Health Organization (WHO) recommends a limit of 70 dB (decibels) to avoid the risk of hearing loss with long-term exposure. But persistent noise pollution at lower levels can have less obvious health effects on our nervous systems, often causing a general decrease in a sense of well-being and interference with communication, relaxation, and recreation.

Levels as low as 30 dB can interfere with sleep, and can impair the ability to concentrate in classrooms. Research suggests that learning is affected starting at background sounds levels as low as 35 dB. Above about 50 dB, people express moderate annoyance in outdoor settings, such as when talking with a neighbor, playing with a child, or trying to enjoy a barbecue. At about 55 dB, people begin to express serious annoyance in outdoor living areas, and also moderate annoyance indoors or on school playgrounds.

The ambient levels of around 60-70 dB, regularly measured near Rockridge homes fronting the freeway, are significantly higher than any of these thresholds.

Until the late 1960s — after SR 24 (State Route 24, the freeway through Rockridge) was planned and mostly constructed— there was little awareness that people should be protected from the adverse effects of environmental sound. This changed in 1969 with passage of the National Environmental Policy act (NEPA); creation of the Environmental Protection Agency (EPA) in 1970; passage of the California Environmental Quality Act (CEQA) in 1970; passage of the Noise Control Act (NCA) of 1972; and publication of the WHO Guidelines for Community Noise released in 1980 (and most recently updated in 2000). These regulatory acts began to inform traffic noise regulations adopted by the Federal Highway Administration (FWHA), and now must generally be considered by agencies eligible for federal transportation funding, such as the California Department of Transportation (Caltrans) and the Alameda County Transit Commission (ACTC).

Given what we know about the present noise levels from SR 24, the freeway could not have been built in its current configuration, at least not without noise barriers or other mitigating measures.

Today, sections of SR 24 may be eligible for noise barriers if the sound level at nearby households reaches, or is predicted to reach, 65 dB or higher without a barrier, and a feasible sound wall is predicted to lower the noise level by at least 5 dB at a sufficient number of residences to make its construction cost effective.