A safety solution for quiet vehicles


The rising number of electric and hybrid buses has brought to light new safety concerns regarding road users, particularly the blind and partially sighted. The reduced audibility of these quiet vehicles means that road users may not hear the vehicle approaching, potentially increasing road accidents.

A recent UNECE regulation has come into place stipulating that quiet vehicles should be fitted with an acoustic vehicle alerting system (AVAS). The Ardent V-AVAS is specifically designed for electric and hybrid buses and coaches to emit a sound that warns road users of the direction, speed and location of quiet vehicles.


The V-AVAS links directly with the CAN-Bus interface to determine state and speed. 

Custom kit

The system can be supplied with Ardent’s V-AMP Power Amplifiers, speakers and wiring harness, as per customer requirements. 

Compliant with R138

Designed in accordance with UNECE Regulation No. 138 for Quiet Road Transport Vehicles.

Rear speakers

Rear speakers can be fitted to allow for directed audio when the vehicle is reversing.

About UNECE Regulation No. 138

The United Nations Economic Commission for Europe (UNECE) brought into effect UNECE Regulation No. 138 for Quiet Road Transport vehicles with regards to their reduced audibility. The regulation looks to have all new types of quiet vehicles fitted an AVAS, with every vehicle type requiring testing and approval.

The regulation requires that all manufacturers install an AVAS system in new types of quiet electric and hybrid electric vehicles from July 2019, and all quiet electric and hybrid electric vehicles from July 2021.

How the Ardent V-AVAS Works

The Ardent V-AVAS has been developed in collaboration with Transport for London (TfL) and is the result of extensive research and testing. Ardent offers a selection of sounds, including the sound developed by TfL for used in the London area, or the customers can supply their own sound, which can be programmed into the system.

The audio recording is factory programmed into the V-AVAS system, corresponding to a speed of 10 km/h. The system reduces or increases its playback speed automatically in proportion to the vehicle’s speed, at a rate of 0.8% per km/h. The sound level remains constant from 0 km/h to the specified speed, then decays away to nothing.

A frequency shift is also specified, meaning that the tonality of the sound changes with vehicle speed. This simulates a change in sound during acceleration or deceleration.

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