The buses are so quiet that TfL fears cyclists and pedestrians – particularly blind or partially sighted people – will be at risk if they cannot hear them coming.
The music will play until the bus reaches 12mph, or when it is reversing or stationary at bus stops. When travelling above 12mph, the bus makes enough noise that an alert is unnecessary. The pitch of the sound will vary with the bus’s speed, helping people know where it is and which direction it is going. The sound has been developed with input from London TravelWatch and accessibility, walking and cycling groups. Bus drivers, bus firms and union officials have also contributed.
The initiative is part of TfL’s Vision Zero initiative to reduce to zero the number of road deaths and serious injuries in London by 2041.
Claire Mann, director of bus operations at TfL, said: “This 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.”
Feedback from road-users, residents, passengers and drivers across all routes will be gathered. The bus sound is part of an acoustic vehicle-alerting system that will be mandatory for all new quiet-running vehicles after September 2021.
However, Unite the Union has warned the trial’s spaceship-like noise sounds nothing like a bus so won’t improve safety.
The union said in a statement it was initially consulted on some potential sounds for London buses but firmly rejected the ones suggested as they did not sound like a bus.
John Murphy, Unite lead officer for London buses, said: “Unite recognises that it is imperative that the new electric buses make a clearly audible sound for safety reasons. However, we believe that the sound chosen is potentially dangerous as it sounds nothing like a bus.
"In a world where people are increasingly distracted when walking, due to the use of electronic devices it is essential that there is a clear and obvious sound of a London bus. If people hear the spaceship sound they won’t think ‘bus’ and could place themselves unintentionally in danger."
He said Unite is also concerned that drivers have not been widely consulted about the new sound and there are potential concerns about whether they will find it distracting or if it will affect their health and urged TfL to pause the rollout of the new sound, undertake a wider consultation with all stakeholders "and agree a sound like a bus".