Adaptive AVAS to improve electric vehicle safety

adaptive AVAS

SINTEF is evaluating the benefits of an adaptive AVAS programme as an improvement on the existing regulations.

AVAS (Acoustic Vehicle Alerting System) is an artificial sound implemented on some of the electric vehicles (EV) on the market today. The main reason for implementing AVAS and adaptive AVAS is to warn pedestrians and cyclists, and especially the blind and poor-sighted of the presence of an almost silent vehicle at low speeds.

Regulations

There are currently two international regulations on the minimum sound requirements for vehicles covering AVAS; UN ECE Reg.1381 on Quiet Road Traffic Vehicles and the FMVSS 1412 in the USA. In both of these regulations, a measurement method is defined, ISO 16254 (ECE Reg.138) or SAE J2889-1(US.). The ISO and the SAE methods are identical, whereby the pass-by noise is measured at 2 m and at speeds up to 20 km/h. Thus far, implementation of adaptive AVAS in EVs or hybrids is not mandatory, but as an optional equipment for some of the EV manufacturers like VW and BMW.

Most of the cars with AVAS have a pause switch, allowing the driver to disengage the AVAS. From 1 July 2019, all new type approvals of EVs and hybrids must include AVAS and the option of a pause switch will be abandoned. The current regulations on AVAS have design criteria on the minimum sound levels, both related to the overall levels at 10 and 20 km/h (up to 32 km/h in America) and the frequency levels in one third octave bands. In addition, a frequency shift is specified, meaning that the tonality of the sound changes with vehicle speed. This is to simulate a change in the engine sound we have on a diesel/petrol car during acceleration. The UN regulation specifies a minimum sound level of 56 dB(A) (2 m distance) at 20 km/h, and a maximum of 75 dB(A) (at any speed). However, it does not mention anything about implementing an adaptive AVAS level depending on the level of the background noise.

High density of electric vehicles in Norway

Norway has the highest density of electric vehicles in the world, due to both user and economic incentives. Currently, there are approximately 180,000 pure electric vehicles on Norwegian roads. In 2018, more than 50% of the new cars sold every month were either pure electric or plug-in hybrid electric vehicles.

This high density has also raised concerns from the Blind Union of Norway. According to this union, about one third of their members now claimed to be more afraid to move around in traffic due to the increased number of quiet vehicles, leading to calls for a mandated adaptive AVAS scheme. No formal statistics are currently available of any serious injuries between these vehicles and pedestrians/bicyclists. By the end of 2017, only two fatal accidents were recorded involving EVs and not one of these involved pedestrians; only drivers or passengers. However, there have been reports of near misses; on one occasion, a blind person was stepping out into a zebra crossing with his white stick, however, an electric car came driving straight past and due to his inability to hear he was nearly knocked over, resulting in the breaking of his stick.

A survey on AVAS in Norway

In 2017, a survey among members of the association of electric cars in Norway was conducted. The survey was sent out to 6,728 members who were asked about AVAS technology and their experiences and perception of AVAS. A total of 3,280 (48,8%) replied which is considered as a successful rate.

Since adaptive AVAS is not yet mandatory on EVs, the survey showed that approximately one third of the EVs do have AVAS installed. The owners were asked a wide range of questions relating to the use of AVAS, especially if they had experienced any dangerous situations with pedestrians/bicyclists due to the low noise levels (at low speeds). The results showed that 83% answered that they had never experienced this type of danger, 6% once and 11% more than once.

The most interesting statistic was that a majority (87%) of those without AVAS had never experienced any dangerous situations, compared to 75% of those who have AVAS.  This may indicate that AVAS, as it is designed today, do not have any major influence on the safety situation for pedestrians/bicyclists. This is the main reason a test programme on adaptive AVAS was designed.

Test programme of adaptive AVAS

In the project funded by the Norwegian Directorate for Children, Youth and Family Affairs (BUFdir) on adaptive AVAS, two hypotheses were tested:

  1. Could the level of AVAS be decreased (from the present value of minimum noise), when the surrounding background noise levels are very low?
  2. Is the current level of AVAS sufficient to warn pedestrians in an environment with high background noise levels, like in a busy urban road?

In order to achieve reproducible and repeatable results, it was decided to mount a loudspeaker in front of the electric vehicle, using a recorded AVAS sound level at 20 km/h. The adaptive AVAS could be adjusted to a fixed sound level during the test. In addition, a loudspeaker was placed behind the people involved in the test. The location chosen for the test had a low-normal background noise level in the range of 37-40 dB(A). The test program included a standard light vehicle with a diesel engine as a reference situation and then different combinations of the sound level of AVAS (50 to 60 dB(A)) and different levels of the background noise level (40-65 dB(A)).  For each test combination, a panel of four people – including both blind/partially sighted and blindfolded but non-blind people pressed a button each time they could hear the vehicle approaching, see figure 1. Each test condition was repeated five times for reducing the statistical variations. A total of three blind and five non-blind people took part in the test panel.

A ‘safe’ distance of 11 m (or 2 seconds) for a vehicle at 20 km/h (5.6 m/s) has been proposed as the necessary distance enabling the vehicle to a full stop, if for example a pedestrian is stepping out to cross a street. All results of the adaptive AVAS  test are analysed with this distance in mind.

Preliminary results

The final report and analysis into the viability of adaptive AVAS have not yet been published; however, the main results are planned to be presented during the InterNoise2019 conference in Madrid, June 2019. Despite this, a preliminary analysis has showed that the tyre/road noise of this particular EV clearly dominates at 20 km/h, even when the original AVAS is turned on, or if an adaptive AVAS at 50 dB(A) is used.  AVAS at this speed and with a low background noise level has no effect on the distance of hearing the car, however the detection distance is always higher than 11 m, due to the audible tyre/road noise. When the background noise level is around 65 dB(A), which is very common in urban traffic situations, and the AVAS level is 60 dB (a typical AVAS level on EVs today), the observed distance of the car is less than 11 m (or 2 seconds) for many of the test persons. This indicates that it would be helpful to increase the level of AVAS with the order of 5 dB under these conditions in order to improve the safety for pedestrians in general.

Truls Berge

Research Scientist

SINTEF Digital

+47 905 72 026

truls.berge@sintef.no

www.sintef.no

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