Noise barriers only effectively block high-frequency traffic sound, not low frequencies

Evidence

Figure 2.17 shows a typical case where a noise barrier is used to mask noise sources, such as vehicles on a highway, to decrease disturbance in the environment. At high frequencies, where the wavelength is small compared to the barrier, shadowing due to the barrier is efficient. At low frequencies, however, the sound waves propagate around the barrier so that the desired masking remains relatively small. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 260

Categorization

• XREF: Explains why highway barriers near residences fail against rumbling truck noise — connects to environmental-noise and urban acoustic design applications.