This note is part of the regulatory structure analysis for the Quiet Towns Project. For the complete hypothesis overview, see Four Research Hypotheses, and for details on complaint gaps, see The Phenomenon of Complaint Gaps.
Introduction
"Why doesn't that loud motorcycle ever get caught?"—many people have wondered this at least once while hearing them roar through residential neighborhoods at night.
The answer is simple: the system for catching them is structurally broken.
This article dissects why loud motorcycles and modified cars cannot be effectively regulated, examining the structure of the legal system. Rather than emotional arguments or personal anecdotes, we aim to find data-driven breakthrough points by visualizing each institutional gap one by one.
Gap ①: Three Laws Are Fragmented in Silos
The loud motorcycle problem spans three different laws.
| Law | Jurisdiction | Coverage |
|---|---|---|
| Road Traffic Act | National Police Agency (Prefectural Police) | Driving behavior, speed, traffic violations |
| Road Transport Vehicle Act | Ministry of Land, Infrastructure, Transport and Tourism/Regional Transport Bureaus | Vehicle structure, modifications, inspections |
| Noise Regulation Act | Ministry of the Environment/Local governments | Noise standards, regulated areas |
The problem is that no single agency can "see the whole picture."
Police regulate driving behavior, but vehicle structure (such as muffler modifications) falls under the Road Transport Vehicle Act. Only regional transport bureaus can issue maintenance orders, so even when police discover illegally modified vehicles on the street, they often lack legal means to address the structural violations alone.
The Noise Regulation Act regulates noise from factories, businesses, and construction work, but vehicle noise during operation is not directly covered. The Ministry of the Environment sets standards but has no enforcement power.
Since three ministries each handle partial responses within their jurisdictions, no entity exists to see the complete picture of the problem.
Gap ②: The "Noise-Free Zone" Based on Engine Displacement
Even for the same type of motorcycle, jurisdiction, noise standards, and inspection requirements differ completely based on engine displacement.
| Displacement | Legal Classification | Inspection | Noise Standard | Reality |
|---|---|---|---|---|
| 50cc and below | Class 1 Moped | None | 84dB (proximity exhaust noise) | Police jurisdiction only |
| 51-125cc | Class 2 Moped | None | 90dB (proximity exhaust noise) | Police jurisdiction only |
| ★ 126-250cc | ★ Light Motorcycle | ★ None | ★ Zero measurement opportunities | ★ Biggest blind spot |
| 251cc and above | Small Motorcycle | Yes (every 2 years) | 94dB (proximity exhaust noise) | Vehicles under old regulations have looser standards |
Light motorcycles (126-250cc) require no inspections, meaning there are no systematic opportunities to regularly check noise levels. This creates the paradox that smaller displacement motorcycles, which are easier to modify, are more likely to become extremely loud in practice.
Furthermore, even for motorcycles 251cc and above, vehicles manufactured before the gradual strengthening of safety standard noise regulations are still subject to the old standards (looser values) that were in effect at the time of manufacture. So-called "old bike groups" are reported to use these transitional measures to ride with exhaust noise levels that would be non-compliant under current standards.
Gap ③: Police Cannot Independently Crack Down on Illegally Modified Vehicles
Illegal modifications violate the Road Transport Vehicle Act and are not traffic violations, so they fall outside the scope of traffic tickets. The authority to issue maintenance orders is designed to rest solely with regional transport bureaus.
In other words, even when police officers discover loud motorcycles on the street and stop them, unless they are working jointly with transport bureaus, their legal means to address illegal modifications are limited. Joint street inspections are conducted, but their frequency and scale do not match the magnitude of the problem.
Gap ④: Maintenance Orders Have Virtually Zero Effectiveness
Even when maintenance orders are issued, their effectiveness faces serious problems.
In 2024 reporting by Kansai TV, a driver who received guidance publicly stated, "I'll fix it today and bring it in, then go home and change it back again."
The current system lacks a continuous tracking mechanism to stop the cycle of correction → temporary fix → re-modification.
Gap ⑤: Peak Damage and Peak Enforcement Are Structurally Misaligned
Loud motorcycle damage is concentrated at night and on weekends.
Meanwhile, street inspections focus on clear daylight hours and prominent locations. Administrative capacity for nighttime on-site response is extremely limited.
During the hours when damage is most severe, enforcement is thinnest. This is not coincidental but a structural consequence of administrative work schedules and budget allocation.
Gap ⑥: No Feedback on Reporting Results
When residents call 110 or file complaints with local governments, the results of reported vehicle enforcement are not shared with residents, citing "confidentiality of investigative matters."
The feedback loop is broken. Residents learn that "even if I report, I never know what happened" and "probably nothing was done." And they stop reporting.
The Complete Picture of the Vicious Cycle
These gaps chain together to form the following vicious cycle:
Within this structure, blaming individual administrative agencies won't solve anything. Police, transport bureaus, and the Ministry of the Environment are all "doing something" within their respective authorities. The problem is that no one is looking at the whole picture.
Breakthrough Points Through Data
This structural vicious cycle has breakthrough points through data.
1. Recording Repeat Violations by the Same Vehicle
With noise sensors + license plate reading (in the future), we can record the fact that "the same vehicle repeatedly passes the same location with loud noise," providing evidence for tracking repeat offenders under maintenance orders.
2. Visualizing Enforcement Time Misalignment
Nighttime and weekend noise concentration data objectively demonstrates that "enforcement is not occurring during the times of highest damage." This provides grounds for proposing resource reallocation by administrative agencies.
3. Mapping Complaint Gap Areas
Showing the geographical divergence between measured noise data and complaint numbers visualizes "the existence of people who don't report" to administrators. Proof that zero complaints ≠ zero problems.
4. Physiological Impact Data on Sensory-Sensitive Individuals
The most important breakthrough point. Recording physiological data (heart rate variability, skin electrical response) of sensory-sensitive individuals can reframe the impact of loud motorcycles from "nuisance" to "medical harm."
Conclusion
Loud motorcycles aren't caught not because "police are lazy" or because "there are no laws." Laws exist. Enforcement exists. But they are fragmented across three ministries, and the problem falls through the institutional cracks.
What's needed to change this structure is not anger, but data. Problems that aren't visualized don't make it onto the policy agenda. Problems not on the agenda don't get budget allocation. Problems without budgets don't get solved.
So first, we measure. We record. We make it visible.
The regulatory structure analysis undertaken by the Quiet Towns Project is the first step in that direction.
References
道路交通法（昭和三十五年法律第百五号）
e-Gov法令検索. デジタル庁
Read source
道路運送車両法（昭和二十六年法律第百八十五号）
e-Gov法令検索. デジタル庁
Read source
騒音規制法（昭和四十三年法律第九十八号）
e-Gov法令検索. デジタル庁
Read source
不正改造車を排除する運動（街頭検査・整備命令の実施状況）
国土交通省. 国土交通省
Read source