A study found that about one-fifth of the US population resides near busy roads that emit higher levels of pollution due to vehicle emissions. In California, 40% of residents live near these roads, the same study found. Exposure to such pollution increases the risk for lung cancer, asthma, and other respiratory diseases. On January 1, more than 100 metropolitan areas will begin installing air pollution monitors near busy roads. This follows new regulations by the US Environmental Protection agency. Monitoring may help in developing further regulations that can help eliminate air pollution in areas where needed.