Research on the influence of traffic conditions on noise level in the passenger compartment of motor vehicles

The research investigates the noise levels measured in the passenger compartments of several automobiles. These vehicles are powered by various engines, travel on various highways, and function at differing speeds and acceleration. The results are visually processed using specialist software. The study investigates the effects of three major sources of automotive noise: engine operation, tire-road contact, and friction between the car body and the air. The immis noise in the passenger compartment is reported to be mostly impacted by the engine’s operational characteristics (load and speed) at lower speeds. In contrast, as travel speed increases, the noise produced by tire-road contact becomes more substantial, and at greater speeds, the noise produced by the interaction between the car body and the air becomes more significant. As a result, the engine type, tire and road characteristics, vehicle speed, and passenger compartment acoustic insulation are all important elements in influencing noise emission in the passenger compartment.


Introduction
The motivation for investigating sounds generated in the passenger compartments of motor vehicles arises from the World Health Organization's suggestion to decrease motor vehicle speeds in urban areas from 50 km/h to 30 km/h.This advice is motivated by the increasing rates of traffic fatalities and the significant environmental degradation caused by pollutants.[1].People frequently experience the impacts of sounds produced by the road transportation system, especially in densely populated urban areas characterized by high-intensity road traffic.Noise pollution originating from vehicle traffic stands as a persistent and significant environmental threat, impacting millions of individuals on a daily basis.
This sort of pollution is caused by frictional forces between moving components, structural elements, or organs in rotational or translational motion during motor vehicle operation.Furthermore, noise pollution occurs during motor vehicle dynamic states when air friction interacts with exterior portions of their bodies or when tires make contact with the ground (highway) [3, pp. 103-118].At the European level, roughly 20% of the population is impacted by car-related sounds [4], revealing a gap in attaining regional noise pollution control targets.The significant noise released by road traffic has a wide range of long-term consequences on human health, causing pain, sleep disruptions, negative effects on the cardiovascular and metabolic systems, and cognitive impairments in children [5].According to the World Health Organization (WHO), approximately 40% of the EU population is subjected to road traffic noise above 55 decibels (dB), motivating continuing study to fully understand the many health impacts of noise [6].The EU Noise Directive of 2003, which has been in operation in all Member States since 1303 (2024) 012050 IOP Publishing doi:10.1088/1757-899X/1303/1/012050 2 2006, specifies a daily noise exposure limit value of 87 dB (8 hours) [4, p. 117].The widespread continuation of high noise levels from road traffic, on the other hand, implies that the aims specified in European laws to reduce noise pollution have not been entirely fulfilled.
Acoustic comfort [7] is defined by the different sounds emitted by motor vehicles, such as engine noises, the movement of rotational or translational organs, frictional forces, tire contact with the ground, and air friction as the vehicle is moving [8, p. 106].The perception of motor vehicle noises by the human ear is dependent on their sound intensity, which can exceed 80 dB and cause health dangers.Figure 1 illustrates the adverse effects of noise on human health.The resonance of mechanical waves inside the structure of the motor vehicle [9], [10], as sensed by passengers at the body level, is referred to as vibrational comfort.The rotational or translational aspects of the car's organs, as well as abnormalities in the surfaces it travels, create these waves.The oscillations of the vehicle must not endanger its structural integrity, the safety of products, or the well-being of passengers since they might cause tiredness and pain [11].Road traffic noise is measured in decibels (dB) [12, p. 1.025] [13], which indicate mechanical vibrations discharged into the environment and conveyed to live beings' auditory organs.For example, the human ear records sound waves with frequencies ranging from 16 to 20,000 vibrations per second and perceives their strength as 0-120 dB.Sound changes in the 30-60 dB range are normal in human conversation.The human ear is unaffected by levels between 20 and 30 decibels, with the top limit accepted by humans being roughly 80 decibels.A sound level of about 130 dB causes acoustic discomfort, whereas levels beyond 150 dB are unbearable to the human ear.

Vehicle noise statistics for reference
Directive 70/157/EEC, published February 6, 1970, encapsulates the basic legislative framework addressing pollution rules for motor vehicles.This regulation, enacted at its inception, introduced pioneering restrictions on noise emissions from motor vehicles, outlining technical specifications that control the quantifiable levels of sound released into the atmosphere during vehicular operation.Over  Note (*) Specific conditions apply to M1 category cars developed from the N1 category.M1 vehicles having a point R more than 850 mm above the ground and a permitted loaded mass greater than 2,500 kg must adhere to the limit values established for the N1 category (where the mass is larger than 2,500 kg but not greater than 3,500 kg).It is important to remember that the raised limit values applicable to off-road vehicles are only applicable to M1 category vehicles when the maximum permissible mass exceeds 2 tons.

3.Results and discussions 3.1 Experiment Concept
Experimentation [15] was carried out on automobiles fitted with compression ignition engines that were within the European pollution limit range of [Euro 3 -Euro 5].The study included three unique routes: a 30-kilometer-per-hour urban route, a 50-kilometer-per-hour urban route, and a 130-kilometer-per-hour extra-urban highway route.The following are the processes for determining the noise level measured in the passenger compartment of a motor vehicle: Reset the dashboard mileage to zero; install a soundlevel meter (Sound-level meter SL-400) on the car; start the engine and begin moving the car from a stop, incorporating acceleration and gear changes, until it reaches the set speed (30 km/h, 50 km/h, 130 km/h); maintain the set speed as consistently as feasible along the authorized route or prescribed travel itinerary, taking into account traffic values and road infrastructure conditions; during the experimental investigation, follow defensive driving guidelines to the greatest degree feasible; conduct tests in the urban area on the same route at both speeds (30 km/h and 50 km/h) and on the extra-urban route (highway) at 130 km/h, covering the same 10 km distance.The Legend: The legal standard is found in Annex II of the Regulation on the Sound Level of Motor Vehicles, which was adopted by the European Commission on April 16, 2014.

Maximum allowable sound limit value dB(A)
Values that are normal and do not exceed the permissible limit Vehicles for passenger transport in the M1 category with a power-toweight ratio of 120 kW/1.000kg 72 Values that exceed the legal limit The measurements were taken during travel on urban routes at speeds of 30 km/h and 50 km/h, as well as on extra-urban routes (highway) at 130 km/h.The centralizer offers a comprehensive overview of the noise pollution levels in these diverse driving scenarios.

Noises made by the Renault Captur 1.5 dCI, euro 5 car's passenger compartment
The results of the analysis of sound evolution measured in the passenger compartment of a Renault Captur 1.5 dCI Euro 5 vehicle are presented below (Figure 2

Noises made by the Volkswagen Jetta 2.0 TDI, euro 4 car's passenger compartment
The results of the analysis of sound evolution measured in the passenger compartment of a Volkswagen Jetta, 2,000 cm3, TDI, Euro 4 automobile are outlined below (Figure 3):    o Maximum sound pressure level: 82.00 dBA Figure 3 illustrates the progression of sound levels (dBA) recorded in the passenger compartment of a Volkswagen Jetta 2.0 TDI, Euro 4 automobile, during both urban and highway travel.

Noises made by the Renault Symbol 1.5 dCI, euro 3 car's passenger compartment
The results of the analysis of the measured sound development in the passenger compartment of the Renault Symbol 1.5 dCI, Euro 3 automobile, are presented below (Figure 4):   but maximum values surpass it.Minimum sound values on the A1 -Sibiu highway match the legal requirement, while maximum and average sound values exceed it.Noise levels in cities fall when traffic speeds decrease from 30 to 50 km/h.The linear sound growth along all three paths shows a rapid increase in levels.B. The trend in the evolution of sound in the passenger compartment of the Volkswagen Jetta, 2,000 cm3, TDI, Euro 4 car, across two urban routes and on the highway, indicates a noticeable upward trajectory.Noise levels rise in direct proportion to speed.At 30 km/h, sound levels on urban highways consistently remain within the limit of 72 dBA.The minimum and average sound levels are within the legal limit at 50 km/h, while the highest values surpass it.Minimum sound values on the A1 -Sibiu highway meet the legal requirement, but maximum and average sound values exceed it.Noise levels in cities drop when traffic speeds decrease from 30 to 50 km/h.On all three pathways, the linear sound progression shows a progressive increase in values.
C. The apparent trend in the evolution of sound in the passenger compartment of the Renault Symbol 1.5 dCI, Euro 3 car, indicates an ascending trajectory along two urban routes and on the highway.Noise levels rise as speed increases.The minimum and average sound levels on urban highways at 30 km/h are under the legal limit of 72 dBA, but the highest levels surpass it.The minimum and average sound levels are within the legal limit at 50 km/h, while the highest values exceed it.Minimum sound values on the A1 -Sibiu highway match the legal standard, while maximum and average sound values exceed it.Noise levels in cities drop when traffic speeds decrease from 30 to 50 km/h.On all three paths, the linear sound growth demonstrates a quick increase in values.
D. The level of noise pollution detected in the passenger compartment is determined by several factors, such as engine speed, tire type and profile, road surface condition, vehicle maintenance status, noise generated by transmission components and organs, vehicle age, physical wear, and fuel type.
E. Decreasing the speed of traffic in urban areas from 50 km/h to 30 km/h leads to a noteworthy reduction in the measured levels of noise pollution in motor vehicle passenger compartments.

Figure 2
Figure 2 illustrates the progression of sound levels (dBA) measured in the passenger compartment of a Renault Captur 1.5 dCI, Euro 5 automobile, during both urban and highway travel.

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When going at 30 km/h on the urban route: o Minimum sound pressure level: 56.20 dBA o 63.9 dBA is the average sound pressure level.o Maximum sound pressure level: 72.00 dBA  When going at 50 km/h on the urban route: o Minimum sound pressure level: 56.10 dBA o Average sound pressure level: 65.60 dBA o Maximum sound pressure level: 75.70 dBA

Figure 2 .
Figure 2. The development of sound (dBA) in the passenger compartment of a Renault Captur 1.5 dCI Euro 5 automobile when traveling on urban (30 km/h, 50 km/h) and highway (130 km/h) routes.

Figure 3 .
Figure 3.The evolution of sound (dBA) measured in the passenger compartment of the Volkswagen Jetta 2.0 TDI is depicted during urban driving at speeds of 30 km/h and 50 km/h, as well as highway driving at 130 km/h.

Figure 2 . 6 
Figure 2. The development of sound (dBA) in the passenger compartment of a Renault Captur 1.5 dCI Euro 5 automobile when traveling on urban (30 km/h, 50 km/h) and highway (130 km/h) routes.

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Figure 4 illustrates the progression of sound levels (dBA) measured in the passenger compartment of a Renault Symbol 1.5 dCI, Euro 3 automobile, during both urban and highway travel.
A. The observed trend in the evolution of sound in the passenger compartment of the Renault Captur 1.5 dCI, Euro 5 vehicle, reveals a consistent increase on two urban routes and on the highway.Noise levels escalate with the increase in speed.At 30 km/h, sound readings on urban roads stay within the regulation limit of 72 dBA.Minimum and average sound values are under the legal limit at 50 km/h,

Figure 4 .
Figure 4.The evolution of sound (dBA) measured in the passenger compartment of the Renault Symbol 1.5 dCI Euro 3 vehicle is presented during urban driving at speeds of 30 km/h and 50 km/h, as well as highway driving at 130 km/h.

Table 2 .
Centralizer employed to concisely present the critical data related to noise pollution identified in the passenger compartments of vehicles equipped with compression ignition engines.This includes summarizing the lowest, average, and maximum values of noise levels. ):