There is much discussion about the benefits of electric trucks in terms of CO2 and NOx and particulate emission reductions. Less is mentioned about the additional benefit of a decrease in sound pollution that should be achievable from an electric truck when compared to its diesel counterpart.
Comparing an electric truck to its diesel brethren, there is still plenty of metal being moved using the same amount of rubber in contact with the ground plus it still has the same ‘brick’ shape when travelling at speed and resulting wind noise to take into account. So, what improvements in noise reduction are possible by switching from a dirty diesel to a clean electric powertrain?
It is worth considering who is hearing the noise at present?
Certainly, the driver of the truck is exposed to its noise all day long. Modern diesel trucks are as well insulated as they can be to protect the driver from Noise, vibration & Harshness (NVH) but there is still around five hundred horses at work with thousands of moving and spinning parts. Any reduction would be welcomed by truck drivers.
It is in urban areas where the general public come into closest contact with truck noise. There are lots of stop, start events which means the truck is under power from start more often and therefore creates more engine noise than when cruising at a speed.
Before we look at the results, it is worth mentioning that decibels (the metric used for noise measurement) is not linear. To explain what that means for noise, a small change in the number of decibels can result in a significant change in the intensity of noise and hence its potential to damage a person’s hearing.
The 3dB ‘trading effect’ means for every 3 dB the sound level increases the impact on hearing health which is doubled. For example, 63 dB(A) is twice as noisy as 60 dB(A). The relevance of this is apparent when considering exposure to hazardous level of noise.
The A-weighting is applied to instrument-measured sound levels (usually using a sound meter device) to account for the relative loudness perceived by the human ear, as the ear is less sensitive to low frequencies. Put simply- A weighting measurements are designed to mimic how humans intuitively perceive noise that is below 100 decibels in volume.
The loudness of the noise is measured in A-weighted decibels and is abbreviated to dBA.
Electric Truck Noise Experiments – MAN Trucks
It was in the area of urban operation that MAN Trucks compared the noise of an electric truck versus its diesel counterpart. The study used microphones on a test track to test noise when reversing, an accelerated pass by, a smooth ride at 20km/h and at 30km/h.
The trucks used in the experiment were a prototype MAN eTruck and a conventional diesel-powered MAN TGX 18.510 of the same weight class. The trucks in question were tractor units with a gross weight of 40 tons. Calibrated hand-held sound level meters were set up on the right and left of the carriageway, each at a distance of 7.5 m.
As Quiet as a Car
“Based on the measurements, the level for the eTruck is about 6 dB lower for steady passing at 20 km/h. If one takes into account here that the diesel truck measured here is about 5 dB quieter at 20 km/h than the typical approach from the literature, the difference between the eTruck and the literature approach increases to 11 dB. The eTruck is thus about half as loud as a classic diesel truck in terms of auditory impression. For the accelerated approach, there was an even more significant level difference between the two trucks of 12 dB,” explains Michael Wirtz, project manager of the measurements at Peutz Consult GmbH. In order to be able to classify the noise development of the MAN eTruck even better, Wirtz draws a comparison with conventionally driven passenger cars: “With a sound power level of approx. 49 dB(A)/m at 20 km/h, the eTruck is only 1dB ‘louder’ than the passenger car with 48 dB(A)/m.”
|New MAN eTruck||MAN TGX 18.510||Difference|
|Reverse (with/without warning tone)||47,8/45,7 dB(A)||60,9/60,1 dB(A)||-13,1/14,4 dB(A)|
|Accelerated pass by||50,4 dB(A)||62,4 dB(A)||-12 dB(A)|
|Smooth ride 20 km/h||48,9 dB(A)||54,7 dB(A)||-5,8 dB(A)|
|Smooth ride 30 km/h||52 dB(A)||56 dB(A)||-4 dB(A)|
Other Truck Manufacturer Studies
The drive-by noise level from a Volvo electric truck reaches 69dB compared to 79dB for a traditional truck. A10dB increase is perceived as twice as noisy. Sister company Renault trucks describe a similar saving for their trucks.
Mercedes quotes a figure of 60 dB for their eActros at 20km/h
It is worth noting that all new electric vehicles in the EU will be required to emit a certain sound level when travelling at speeds below 20 kph. The sound level required depends on the speed and gets higher as it increases. At the maximum speed of 20 kph it should be at least 56 decibels.
In order to enter the low noise zones that have existed for some years, the truck needs to operate at a level below 71bB – no problem for all of the electric trucks mentioned above.