Sizing Earplug Attenuation for Street-Facing Bedrooms: The Reduction Actually Required to Bring Passing-Traffic Peaks Below the Sleep-Disturbance Criterion

Earplugs are bought by their labelled attenuation, but the labelled figure is a laboratory value that real ears, imperfectly fitted at bedtime, do not achieve. This paper computes the reduction actually required in three street scenarios — indoor traffic peaks of 48, 58, and 68 dBA at the bed — against a stated sleep criterion of 45.0 dBA at the ear, applying a stated real-world derating of 0.55 to plug ratings. A foam plug labelled 32 dB delivers 17.6 dB in the model, which is ample for the arterial case, leaving peaks of 40.4 dBA, but on an urban main road the requirement is 23.0 dB and the same plug leaves 50.4 dBA — above criterion. The practical output is a three-line sizing table, and a clear statement of the exposure level at which plugs alone stop being the answer and the window or the room must change instead. This study is simulated, not measured.