Siren volume has risen steadily across a century.

Evidence

Since the introduction of the disc siren in North America, the principal change has been in the volume of sound output. We have measured the siren on a 1912 vintage vehicle at 88 to 96 dBA at 3½ meters. By 1960 siren intensity had risen to 102 dBA at 5 meters. In recent years a new type of yelping siren has been introduced for emergency vehicles, measuring 114 dBA at the same distance. The United States is now manufacturing a yelping siren for police car use which measures 122 dBA at 3½ meters. — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 561

Categorization

• SEED: Concise quantitative thread from 88 to 122 dBA — a strong data hook for an essay on the escalating loudness of emergency signaling.
• XREF: Connects to my interest in measuring noise; gives concrete dBA methodology for cataloging signal-sound intensity. — connects to: Siren loudness has risen from 95 to 122 dBA over a century; Emergency siren loudness proxies track ambient noise rise over decades — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 625; Ocean ambient noise levels have risen dramatically over the past sixty years — George Michelsen Foy, Zero Decibels: The Quest for Absolute…, 354
• corroborated: 2 independent passages support this claim — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 561

Broader Connections

• Emergency siren loudness proxies track ambient noise rise over decades #corroborates (0.90) — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 625
• Ocean ambient noise levels have risen dramatically over the past sixty years #corroborates (0.60) — George Michelsen Foy, Zero Decibels, 354