MELBOURNE: Less noisy cars could be tricking a driver to think he is driving slower than he really is, according to Australian researchers.



Mark Horswill and Annaliese Plooy of Queensland university report their findings in a journal 'Perception'.



"The main design principle of making cars these days to be as quiet as you possibly can, is actually a real problem for road safety," Horswill was quoted saying in ABC report.



He said engineers and car manufacturers reduce the level of noise inside cars because they think it distracts the driver or interferes with the car's entertainment system. However, these latest findings suggest this is a "questionable" claim.

"By doing that you're systematically removing the cues that people are using to judge their speed," he said adding "They're feeling more safe and they're getting a sensation of going slower ... but of course the danger is still there."

In their study, Horswill and Plooy presented participants with pairs of video-based driving scenes and asked them to judge their speed. The participants heard either in-car noise at the level it occurred in the real world, or reduced in volume by 5 decibels.



This is equivalent to the difference between the sound you would hear in a noisy car with the windows down and the sound you would hear in a luxury car with the windows up.



The researchers found that the change in noise shifted people's speed perception. "When the noise in the car is made quieter, people think they're going about 5 kilometres an hour slower than they would otherwise," Horswill said.



Horswill said he first got the idea for the study while driving in a luxury car lent to his research team. "It was the poshest car we ever had," he said.

"We found that we were accidentally going way over the speed limit very very fast, but inside the car it was so nice you barely had any sensation of movement at all," he added.



Horswill said his conclusions are also supported by other studies. He has previously studied people's perception of appropriate speed as they watched video-based driving scenes, from the point of view of the driver.



People were asked whether they would go faster or slower than the videoed driver as the noise of the moving car was adjusted.



"When we turned the car noises down, people chose to drive faster," Horswill said who also studied to show that driver of a high performance car will drive faster than those driving a lower performance car.



"It's pretty clear that if people are given a car that is more powerful then they will drive it faster and more dangerously," he said.