Blind VS able to see
Differences in sound salience between sighted and blind listeners when testing an electric car.
Electric vehicles operate on electric motors powered by silent energy sources, which significantly reduces the noise level from the vehicle compared to cars with internal combustion engines. This has a beneficial effect on the acoustic ecology of cities, but the other side of the coin is the almost silent movement of electric vehicles at low speeds. And paradoxically, at low speeds, electric cars pose the greatest danger. When driving along the roadway in a stream of cars, the main source of noise of any vehicle is the noise of tires rubbing against the asphalt. But when driving through an area filled with pedestrians, such as a courtyard, electric vehicles become invisible and pose a great danger to pedestrians. And if sighted people still have the opportunity to show attentiveness and caution when crossing the road, then for people with visual impairments, an electric car turns into a real acoustic “invisibility”.
The THOR team conducted a series of tests to determine vehicle visibility and compare visibility scores between sighted and blind people. The “vehicle visibility” characteristic is the time between the detection of the vehicle and its passage past the expert. In the following, this characteristic is referred to as “arrival time” and is measured in seconds.
When a vehicle moves at a speed of 40 km/h and above, the main source of noise is the noise of tires rubbing against the road. Therefore, measurements were carried out at speeds from 10 to 30 km/h in increments of 10 km/h, with 4 passes at each speed to average the results. A straight section of road in a low-noise suburban area was selected for measurements. At one end of the road the electric car picked up and began to move at a given constant speed; at the other end of the road there was an expert zone. The experts were provided with event recording remotes, with which they recorded the approaching vehicle. Picture 1 shows the test results, the solid line indicates sighted experts, the dotted line indicates blind experts.
From the data provided, we can conclude that at a speed of 10 km/h, the visibility of the electric vehicle for both groups of experts were practically the same. In the environmental conditions of our tests, the approach time was ~10 s.
And at speeds of 20 and 30 km/h, experts with visual impairments noticed the approaching vehicle one and a half, or even two times earlier than the sighted ones.