Four Research Hypotheses and Verification Plan

This note presents the overall hypothesis framework of the Quiet Cities Project. Please refer to individual notes for details on each hypothesis.

While traffic noise is recognized as a daily environmental stressor in urban areas, its impact is often overlooked as something people "get used to." For individuals with sensory sensitivity, traffic noise can become a serious barrier that prevents them from going outdoors.

The World Health Organization (WHO) recommends in its environmental noise guidelines that annual average exposure levels to road traffic noise be kept below 53dB(A)[1], but many locations along major roads in Japan exceed 70dB.

However, the problem is not solely in the absolute dB values. What actually causes stress in humans is "suddenness," "contrast ratio (gap with silence)," "frequency of repetition," and "semantic meaning of sounds (modified motorcycle sounds, loudspeakers, etc.)," none of which can be captured by current time-averaged indicators.

Furthermore, no research exists worldwide that addresses the outdoor mobility experiences of individuals with sensory sensitivity and misophonia. Misophonia is far from rare: a survey of U.S. undergraduate students found that about 20%[2] reported clinically significant symptoms (Wu et al., 2014), though representative general-population estimates remain limited. It overlaps with the sensory sensitivity seen in ASD and other conditions but is a distinct concept, and this project treats these as separate.

H1: Sensory-Sensitive Individuals × Outdoor Mobility Routes × Physiological Data

People with sensory sensitivity and misophonia tendencies show significantly higher physiological stress responses during urban outdoor mobility compared to the general public, which constrains their frequency of outings and route selection. First research in this field worldwide.

→ Details: How Much Do Sensory-Sensitive Individuals Suffer Outdoors（このサイトの記事）

H2: Zoning Regulations × Noise Disparity (Environmental Justice Hypothesis)

Low-income groups tend to concentrate in affordable housing along major roads, and the severity of noise damage is inversely proportional to income — a form of environmental injustice (the income correlation is established by international research). The direct correlation between disability and arterial-road co-location is sparsely studied, and no systematic empirical work exists in Japan for either correlation. This study treats both as hypotheses, to be verified through field measurement in Phase 2.

→ Details: People Living Along Major Roads Experience Greater Noise Damage（このサイトの記事）

H3: Existence of Complaint Void Zones

Many "complaint void residents" exist who suffer from noise damage but have not filed complaints with authorities, distorting administrative priorities for noise countermeasures.

→ Details: The Phenomenon of Complaint Voids（このサイトの記事）

H4: Context-Dependent Noise Stress

Even with the same dB level of noise, stress responses vary significantly depending on the type of sound and the context in which it occurs. Current dB averaging indicators are insufficient as proxy indicators for sensory stress. As part of the Phase 2 research plan, the lab is exploring a Contrast Index (CI) sketch that composes contrast with background noise, repetition frequency, time-of-day weighting, and a sound-source mask coefficient (see the H4 essay for details).

→ Details: What dB Alone Cannot Measure（このサイトの記事）

What Should Be Done

• Real-time physiological and subjective data collection during outdoor mobility of sensory-sensitive individuals
• Japan's first empirical study on zoning × noise disparity
• Mapping complaint void zones and categorizing "reasons for not reporting"
• Development of context-dependent sensory stress indicators
• Creation of policy recommendation reports integrating the above

What Doesn't Need to Be Done

• Indoor acoustic measurements (sufficient accumulation by Sakuma, Matsui, and others)
• Re-proving that "noise is bad for health" (already confirmed by WHO)
• Creating noise maps using only dB (Ministry of Environment's national noise map exists)
• General theory of noise × real estate value (already established by Poznan research, etc.)

This section organizes 15 research notes by type.

Essays (essay-)

• Who to Change What For — Three-Layer Target Audience Design（このサイトの記事）
• What dB Cannot Measure — The Concept of Context-Dependent Stress（このサイトの記事）
• Why Victims Stay Silent — The Social Psychology Behind the Failure of Collective Noise Complaints（このサイトの記事）
• The Complaint Gap Phenomenon — Why 'Reporting Won't Change Anything' Is Rational（このサイトの記事）
• Assessment Never Reaches the Field — Why Environmental Impact Assessment Fails to Control Road Noise（このサイトの記事）
• EVs Are Too Quiet — The Paradox of Mandatory Acceleration Sound and Type Certification（このサイトの記事）
• Inside the Perpetrator Group — Why Self-Regulation Fails in the Noise Industry（このサイトの記事）
• Theory of Change — From Personal Pain to Transforming Urban Design（このサイトの記事）
• Those Living Along Arterial Roads Bear the Greatest Noise Burden — An Environmental Justice Hypothesis for Japan（このサイトの記事）
• Why Loud Motorcycles and Modified Cars Aren't Caught — Structural Analysis of Noise Regulations（このサイトの記事）
• How Much Do People with Sensory Hypersensitivity Suffer Outdoors — A World-First Research Gap（このサイトの記事）

Case Studies (case-)

• Soundproofing Subsidies Choose Their Roads — The Disparity Structure of the Roadside Housing Soundproofing Program（このサイトの記事）

Institutional, Judicial, and International Comparisons

• A Proposed Industry Responsibility Clause for the Municipal Soundscape Ordinance Model（このサイトの記事）
• The Learning Curve of Nine Noise Lawsuits — From the Tolerable Limit Doctrine to a ¥5.9 Billion Verdict（このサイトの記事）
• WHO 2018 Environmental Noise Guidelines vs. Japan's Standards — What a Gap of Up to 25 dB Actually Means（このサイトの記事）

References

Environmental Noise Guidelines for the European Region — World Health Organization (WHO). WHO Regional Office for Europe

Auditory and non-auditory effects of noise on health — Basner, M. et al.. The Lancet, 383(9925), 1325-1332

騒音に係る環境基準について（告示） — 環境省. 環境省

Architecture for Autism: Concepts and Built Environment — Mostafa, M.. Archnet-IJAR, 8(1), 143-158

聴覚過敏と暮らしの音環境 — 佐久間哲哉. 日本音響学会誌, 77(5), 296-301

発達障害に伴う聴覚過敏と音環境に関する実態調査 — 松井温子・佐久間哲哉. 日本建築学会技術報告集, 26(62), 169-172

Misophonia: Incidence, Phenomenology, and Clinical Correlates in an Undergraduate Student Sample — Wu, M. S. et al.. Journal of Clinical Psychology, 70(10), 994-1007