Living Near Highways and Air Pollution

https://www.lung.org/clean-air/outdoors/who-is-at-risk/highways

The area most affected, they concluded, was roughly the band within 0.2 to 0.3 miles (300 to 500 meters) of the highway.

小于300 反而影响不大？

应该说的是以高速中间隔离带为中心，两边300-500米距离内的这一个范围。毕竟高速限速不同，车道数量不同，这个距离会有些区别。