The Infiniti M35h will become the world's first hybrid to feature an audible pedestrian warning system when it goes on sale. The ground-breaking high performance hybrid, which can travel further and faster in silent electric-only mode than other hybrids, utilizes a range of distinctive sounds to ensure the safety of other road users.
The new Approaching Vehicle Sound for Pedestrians (VSP) system - is computer-controlled and links an in-car synthesiser with a speaker built in to the front bumper. It automatically works from start-up to 30km/h, cutting back in at 25km/h as the vehicle slows.
Instead of just a single tone, a range of high-low sounds at different volume levels was chosen after an extensive research program to find the most effective, but least intrusive noise.
The team developing the system in Infiniti's parent group worked with cognitive and acoustic psychologists studying areas from pedestrian behavioral patterns to noise pollution.
The result is a sine-wave that extends from 2.5kHz at the high end to a low of 600Hz. It is a range readily audible to all age groups, while avoiding a sound range (around 1,000Hz) that would add unnecessary noise to the environment.
The noise sweeps from high to low frequency depending on vehicle speed and whether the M35h is accelerating or decelerating.
It is loudest at start-up to give a clear indication the vehicle is beginning to move off, while an intermittent tone is used when reversing - both sounds were calculated to ensure the M35h cannot surprise pedestrians or the visually impaired as it approaches.
Although the M35h can travel at speeds of around 80km/h on noise-free electric power alone, road noise past 30km/h means the M35h generates sufficient sound for the Approaching Vehicle Sound for Pedestrians to shut off. An extensive testing program during the hybrid's development showed that, in mixed driving conditions, the M35h was able to drive in electric-only mode for as much as 50% of the time.