The Australian registered vehicle fleet has increased by nearly 16% since 2004 and now numbers 15.7 million vehicles as at March 2009. The average annual rate of growth over that period has been 3%. Passenger vehicles and light commercial vehicles make up over 14 million vehicles.

Traffic noise is almost certainly the most pervasive type of noise pollution in Australia with 40% of the polulation subjected to undesirable levels of noise pollution and 10% exposed to excessive levels. A 2001 report by the NRTC (National Road Transport Commission) showed Australian regulations allow up to double the noise levels from some vehicles in comparison to Japan, Europe and the US.

Poor urban planning with homes, schools, hospitals and other community buildings built along roadways together with an increase in traffic volumes have led to noise pollution becoming a serious problem.

At low speeds, typical of our modern urban road systems, traffic noise is mostly generated by vehicle engines, exhausts, transmission and braking. Start stop traffic conditions add to the problem. In a report into noise in NSW in 1999, street traffic noise measured at 40km/h from a 7 meter distance is 75 decibles and is considered 'noisy'. Trucks measured under the same conditions have a noise level just under 90 decibles which is considered 'very noisy' (being of a similar level to pneumatic drills).

On freeways with more constant speeds noise is more typically generated through tyre contact with the road and aerodynamic drag over the vehicle.

In comparison to the noise levels of internal combustion engines (ICE) electric vehicles create little noise other than the hum of the electric motor and tyre noise. This has raised some safety issues have been raised for the blind and visually impaired.

At speeds above 30km/h tyre and aerodynamic noise from electric vehicles is sufficiently audible for pedestrians, according to a study by University of California. Below this speed there may be issues for pedestrians.

"Frankly, we've been working for 30 years to make cars quiet -- never thinking they could become too quiet," said Robert Strassburger, vice president for vehicle safety at the Alliance of Automobile Manufacturers. Nissan engineers are currently working on the issue for the forthcoming Nissan Leaf.

It would be ironic indeed if vehicle noise pollution was enshrined in legislation without a full appraisal of the benefits and risks. Care must be taken to ensure that low speed sound from electric vehicles does not compromise the benefits their quiet operation bestows.

This topic raises many questions - how loud an artificial sound should be? does it cut out at higher speeds? should individuals be allowed to customise it? (imagine the consequences), should a global standard be introduced? should compulsory sound also be enforced for bicycles?

Whatever the outcomes of this safety issue, electric vehicles are set to quieten our city streets, a change that will be welcomed by most.