London to trial new sound-generation system on its ‘quiet’ electric buses


In an initiative to increase safety for all road users, Transport for London (TfL) has created an innovative new bus sound for its electric and hybrid buses that is set to be trialled on the UK capital’s latest zero-emission bus route from January next year.

TfL has developed the sound, which is played through special speakers inside the front of the bus, to ensure that all road users are aware of the presence of its fleet of zero-emission buses when they are moving at slow speeds. Without this sound, these vehicles are almost silent which could pose a safety risk, particularly for people who are blind or are partially sighted. The sound has been developed with input from Guide Dogs for the Blind, London Travelwatch and other key accessibility, walking and cycling groups, which has helped ensure that it accommodates the needs of all road users including pedestrians and cyclists, children and disabled people. Bus drivers, operators and union representatives have also provided input.


The sound will play until the bus reaches 12mph (20km/h), or when it is reversing or is stationary at bus stops. When travelling above 12mph, the bus will make enough noise that an alert is unnecessary. The pitch of the sound will vary with the speed of the vehicle, helping people know where the bus is and which direction it is going. The sound will be trialled first at varying volumes on the 100 bus route over a six-month period from January. It will also be trialled on other routes, including the C10 route from March, and the P5 route from May, as new zero-emission vehicles are introduced. Feedback from cyclists, residents, passengers and drivers across all routes will be collected to help develop the most effective system for all road users.

The artificial bus sound is one aspect of TfL’s world-leading Bus Safety Standard, which is already improving safety on London’s roads by requiring technology that automatically limits the speed of buses and increased mirrors and cameras. The new artificial bus sound is part of an acoustic vehicle alerting system (AVAS) that will mandatory for all new ‘quiet’ running vehicles to use a system after September 2021. AVAS will be consistent across all London bus operators and will be available to transport providers across the UK to ensure that people can detect and recognise a bus regardless of where they are in the country.

“Improving local air quality in London is a vital priority and will improve life for everyone, particularly those walking. But as our buses become cleaner and quieter, it is important that pedestrian safety is not compromised,” commented, Stephen Edwards, director of policy and communications at Living Streets. “TfL’s trial of noise-emitting zero-emissions buses is a welcome step in ensuring that greener vehicles are equipped to be safe for everyone, particularly older people and pedestrians with sight impairments.”

Claire Mann, director of bus operations at TfL “Trialling AVAS in the following months will ensure the system is best equipped to alert all road users to the presence of quiet running buses, preventing collisions, and making deaths and serious injuries on our roads a thing of the past.”


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Adam joined the company in 1994, and has been News Editor of TTT since 2009. In his other role as Circulation Manager, he helped create the original Traffic Technology International distribution list 23 years ago, and has been working on it ever since. Outside of work, he is a keen fisherman, runs a drumming band, and plays an ancient version of cricket.