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.

Background

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)(external site, opens in a new tab) 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, our September 2026 Europe PMC searches returned no research addressing 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(external site, opens in a new tab)), 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.

Four Research Hypotheses

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. A field where we found no prior research.

→ Details: How Much Do Sensory-Sensitive Individuals Suffer Outdoors

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

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

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

Research Gap Certainty Ranking

What Should Be Done / What Doesn't Need to Be Done

What Should Be Done

• Real-time physiological and subjective data collection during outdoor mobility of sensory-sensitive individuals
• An empirical study on zoning × noise disparity (our searches found no prior Japanese study)
• 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.)

Related Research Notes

This section organizes 15 research notes by type.

Essays (essay-)

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

Case Studies (case-)

• Soundproofing Subsidies Choose Their Roads — The Disparity Structure of the Roadside Housing Soundproofing Program

Institutional, Judicial, and International Comparisons

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