This note is part of the regulatory structure analysis for the Quiet Towns Project. For the complete hypothesis overview, see Four Research Hypotheses; for the siloed structure of regulation, see Why Loud Motorcycles Aren't Caught.
What Is Happening
As electric two-wheelers and electric vehicles spread through cities, a new contradiction has entered the urban noise debate. One might expect that more silent vehicles would reduce traffic noise — yet international vehicle safety regulation has instead classified "excessive quietness" itself as a risk, and mandated the addition of artificial driving sounds.
United Nations Economic Commission for Europe (UNECE) Vehicle Regulation No. 138 (R138) requires electric vehicles to be fitted with an AVAS (Acoustic Vehicle Alerting System) — a mechanism that emits a minimum sound level at speeds below 20 km/h. In Japan, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) amended the safety standards under the Road Transport Vehicle Act (道路運送車両法, Act No. 185 of 1951) and has made AVAS mandatory on new electric vehicles approved from 2021 onwards.
The problem is that this "add-noise regulation" partially contradicts the direction of reducing urban noise. Environmental policy has framed quiet vehicles as socially desirable — and the safety counterargument that "too quiet means dangerous" now collides with it head-on.
Background and Context
AVAS regulation originates in pedestrian and cyclist safety. Human perception conditioned to internal combustion engines has long relied unconsciously on engine sound as a signal that "a vehicle is approaching." A growing body of research evidence shows that the absence of this signal raises collision risk for visually impaired people, older adults, and pedestrians distracted by smartphones.
European Commission Regulation 540/2014 made AVAS mandatory on new type-approved electric vehicles from July 2019. The minimum standard requires 56 dB(A) or above at speeds below 20 km/h, with the sound required to vary with vehicle speed.
In Japan, Article 43-4 of the Road Transport Vehicle Act safety standards (Electric Vehicle Approach Warning System) has been established, and compliance with sound level and tone requirements is verified during type certification review. However, the actual degree to which AVAS contributes to ambient noise levels has not been systematically aggregated in domestic environmental noise data.
Reading the Structure
The problems that AVAS regulation brings to light fall into three layers.
The first is the asymmetry between minimum and maximum sound level design. R138 establishes a minimum sound level but sets no upper limit (or an extremely loose one). Manufacturers therefore retain latitude to choose near-maximum sound levels in order to project a sense of "power" for buyers. In the electric sports motorcycle category in particular, products have appeared that intentionally add a forceful sound profile to differentiate from internal combustion engine vehicles. If the regulatory purpose is pedestrian protection, the absence of an upper limit creates a loophole that permits operation divorced from that original intent.
The second is the divergence between type certification and actual use. There is no institutional exclusion of the possibility that the AVAS sound level and tone compliant at type certification could change after sale through software updates or replacement with aftermarket components. The same problem seen with internal combustion engine muffler modifications is liable to recur in the form of post-sale AVAS configuration changes for electric vehicles.
The third is the absence of a policy evaluation axis for the quieting effect. The environmental noise evaluation framework managed by the Ministry of the Environment — the LAeq time-average metric — treats the steady-state sound that AVAS adds at low speeds and the acceleration noise produced by internal combustion engines under the same indicator. Yet their impacts on the residential environment are qualitatively different. The value of eliminating sudden noise events caused by acceleration sounds in residential neighborhoods at midnight is not something LAeq averaging can capture. No method exists within the current noise policy framework to assess the net impact of EV adoption on the urban sound environment.
The ContrastIndex proposal discussed in What dB Cannot Measure connects to this evaluation problem. Because mandatory AVAS sound is low-speed and steady-state, it has low "suddenness" and low "contrast against ambient noise." Only by shifting the evaluation metric from time-averaging to outlier event detection can the quieting effect of EV adoption be properly assessed.
References
騒音に係る環境基準について（環境庁告示第64号） — 環境省. 環境省
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
Illegal Vehicle Modification Elimination Campaign (Street Inspection and Maintenance Order Implementation Status) — Ministry of Land, Infrastructure, Transport and Tourism. Ministry of Land, Infrastructure, Transport and Tourism
Environmental Noise Guidelines for the European Region — World Health Organization (WHO). WHO Regional Office for Europe