From next year, some of London’s electric buses will play artificial noise while traveling at low speeds, and the specific sound that’s been created for them is an ambient treat for the ears. The noise was created by Zelig Sound, which has been working with Transport for London on the audio over the past year.

The sound is being introduced in response to a new EU law which stipulates that all electric vehicles will eventually need to produce artificial noise while traveling at low speeds, to make up for the lack of noise from their internal engines. If you can’t hear a vehicle, then you’re not as aware of its presence, and research suggests pedestrians are more likely to be hit by electric or hybrid cars as a result.

Wired reports the base note is a soft F#maj7 chord, with a slight pulsing sound in the background. This is what gets played when a bus is stationary:

Then, when the bus starts moving, the chord is joined by a C sharp every three beats to indicate motion:

In the EU, regulations mean that cars will need to play a sound that’s 56 dB in volume when traveling at less than 20 km/h (12.4 mph) — any faster and a combination of tire and wind noise makes up for the lack of engine noise.

Since the artificial sound doesn’t have to be retrofitted into older electric cars until 2021, London’s transport authority is introducing the new bus sounds gradually. The capital’s 100 route will get the new sounds for six months starting in January, before it expands to the C10 and P5 routes later in the year. Its introduction follows field trials in Tottenham, where its effectiveness has been tested with real world pedestrians. Organizations representing people with visual impairments, cycling, and environmental groups were also consulted during its creation.

Of course, the real question now is not how the track sounds in isolation, but how it comes across when multiple electric buses are jockeying for space on London’s busy streets. Only 200 of London’s roughly 8,000 iconic red buses are currently electric, but that number is only going to increase as more of the capital’s combustion-engine-equipped vehicles reach the end of their lives.