INTERNATIONAL SCIENTIFIC JOURNAL "TRANS & MOTAUTO WORLD" WEB ISSN 2534-8493; PRINT ISSN 2367-8399

Ride comfort in road vehicles: a literature review

Diana Dacova
Technical University of Sofia, Bulgaria
ddacova@tu-sofia.bg

Abstract: Passengers and the driver in vehicles are subjected to vibrations, noise, acceleration, etc., which affect the comfort, activity and
health of people. The effect of vibrations on the human body depends on their frequency, amplitude, duration and direction of impact.
Prolonged exposure to vibration causes fatigue in the driver and passengers, which reduces their performance and worsens their functional
condition. This can affect traffic safety, so one of the main requirements for modern vehicles is to increase ride comfort. T he ride comfort is a
set of conditions, impacts and sensations of the driver and passengers when traveling in vehicles. Over the years, there have been many
studies and scientific developments aimed at measuring, evaluating and analysing the various factors that affect ride comfort. This paper
presents a review on the research studies that have been done on dynamic factors that affect the ride comfort in road vehicles and methods
used for measurement and its evaluation were discussed. Finally, some existing suggestions for improving the ride comfort in road vehicle
are presented.
Keywords: RIDE COMFORT, ROAD VEHICLES, MOTION SICKNESS, VEHICLE VIBRATION, ACCELERATION

In [5] is noted that when humans exposed to interference with

1. Introduction
certain frequencies, resonant phenomena occur, which must be
Nowadays, people spend most of their time traveling by private considered in the vibrations of the driver, operator and passengers.
or public transport. Passengers and the driver in vehicles are The resonant frequencies of the human body are eyes 12–27 Hz;
exposed to vibrations, noise, acceleration, etc., which affect the throat 6–27 Hz; chest 2–12 Hz; legs, arms 2–8 Hz; head 8–27 Hz;
comfort, activity and health of people. The effect of vibrations on face-jaw 4–27 Hz; lumbar part of the back 4–14 Hz; stomach 4–12
the human body depends on their frequency, amplitude, duration Hz. At significant vibration values in the frequency range 4–10 Hz,
and direction of impact. Prolonged exposure to vibration causes the person may feel painful sensation and discomfort due to
fatigue in the driver and passengers, which reduces performance resonant oscillations of the “breast-stomach” system. According to
and worsens their functional condition. This can affect traffic the authors of [4, 5] vibrations with a frequency of 3–5 Hz cause
safety, so one of the main requirements for modern vehicles is to reactions of the vestibular apparatus and can cause motion sickness.
increase the ride comfort. Over the years, there have been numerous It is important to study the effects of vibrations on the human
studies and scientific developments aimed at measuring, evaluating body and their consequences is to study the mode of head
and analysing the various factors that affect ride comfort. vibrations. Regardless of the direction of disturbance (vertically or
The comfort is subjective state of well-being or absence of horizontally), the head always makes movements in space with an
mechanical disturbance in relation to the induced environment elliptical trajectory. In [6] the author notes that nodding head
(concerning mechanical vibration or repetitive shock) [1]. The car movements have a resonant frequency of 2 Hz and vertical ones 8–
passenger comfort is determined by the complex impact of many 27 Hz. According to the author, the human vestibular apparatus also
factors, which can be separated in the following areas [2, 3]: responds to low-frequency vibrations and the symptoms of motion
• dynamic factors influencing the ride comfort (mechanical sickness appear at a frequency of 0.5–1.3 Hz.
comfort - vibrations with low and very low frequency, shocks and There are many international standards for assessing the
accelerations) and the levels of vibrations with high frequency and vibrations to which a person may be exposed. The international
noise (vibroacoustic comfort); standard ISO 5349-1:2001 “Mechanical vibration – Measurement
• the microclimate in the passenger compartment (cabin) of the and evaluation of human exposure to hand-transmitted vibration –
vehicle (thermal comfort, air quality, atmospheric pressure, etc.); Part 1: General requirements” refers to the measurement and
• and factors depending on the ergonomic position of the passengers. assessment of the impact of vibrations transmitted to the human
The driver and passengers assess the ride comfort subjectively hand [7]. The second part of this standard is a practical guide for
based on their own feelings. measuring human hand vibration in the workplace: ISO 5349-2:
This paper reviews research on the dynamic factors that 2001/Amd 1:2015 “Mechanical vibration – Measurement and
influence the vehicles ride comfort, methods for its evaluation and evaluation of human exposure to hand-transmitted vibration – Part
suggestions for its improvement. 2: Practical guidance for measurement at the workplace –
Amendment 1” [8]. Another international standard for the
2. Impact of Vibrations in Vehicles on Passengers assessment of mechanical vibration is ISO 10326-1:2016
“Mechanical vibration – Laboratory method for evaluating vehicle
The ride comfort depends on the characteristics of the forces seat vibration – Part 1: Basic requirements”. ISO 10326-1:2016
that cause oscillations and vibrations, on the design of the car, the applies to specific laboratory tests on seats that assess the
parameters of the suspension, the driving conditions etc. The forces transmission of vibration to passengers in any type of seat used in
that cause low-frequency vibration (oscillations) and high- vehicles and mobile off-road vehicles. It shall specify the test
frequency vibrations of the car arise because of internal (unbalanced method, the instrumentation requirements, the measurement
rotating masses of the engine and transmission, uneven engine evaluation method and the method of reporting the test result [9].
operation) and external causes (uneven roads). The second part of the international standard ISO 10326 is ISO
The unpleasant and harmful effects of vibrations on human 10326-2:2001 “Mechanical vibration – Laboratory method for
being depend primarily on the way they are transmitted to the evaluating vehicle seat vibration – Part 2: Application to railway
human body and on the transmission of vibrations in the body, on vehicles”. It concerns tri-axial rectilinear vibration within the
the physical nature of vibrations, on the time a person is exposed to frequency range 0.5 Hz to 50 Hz [10]. Another standard for comfort
vibrations and from the individual characteristics, etc. assessment is the standard BS EN 12299:2009 “Railway
The vibrations of the car in real road conditions are varied, and applications. Ride comfort for passengers. Measurement and
the sprung mass can receive low-frequency 1–3 Hz, high-frequency evaluation”. This standard specifies methods for quantifying the
7–15 Hz, vibration 15–30 Hz and complex shocks. The human effects of vehicle body motions on ride comfort for passengers and
driver or passenger is also a system with a fundamental frequency vehicle assessment with respect to ride comfort [11].
of free vibrations, which is in the range of 3.5-5 Hz. The human The main document for vibration assessment is the international
being is adapted to exposure with a frequency of about 1 to 2 Hz standard ISO 2631:1997 “Mechanical vibration and shock -
corresponding to the frequency of the everyday walking [2, 4]. Evaluation of human exposure to whole-body vibration”. It consists

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of five parts: Part 1: General requirements [ISO 2631-1:1997/Amd

1:2010]; Part 2: Vibration in buildings (1 Hz to 80 Hz) [ISO 2631-
2:2003]; Part 3: Evaluation of exposure to whole-body z-axis
vertical vibration in the frequency range 0.1 to 0.63 Hz [canceled
and replaced with International Standard ISO 2631-1:2010]; Part 4:
Guidelines for the evaluation of the effects of vibration and
rotational motion on passenger and crew comfort in fixed-guideway
transport systems [ISO 2631-4:2001/Amd 1:2010]; Part 5: Method
for evaluation of vibration containing multiple shocks [ISO 2631-5:
2018]. The international standard ISO 2631-1 repeals and replaces
the first edition ISO 2631-1:1985, as well as ISO 2631-3: 1985. The
revised edition of this part of ISO 2631 combines the new
experience and research results published in the literature. In this
revised edition, the frequency range is extended below 1 Hz. The
main objective of ISO 2631-1 Part 1: General requirements is to Fig. 1 Scheme of the relation between the vestibular apparatus and other
define methods for the quantification of whole-body vibrations in organs of external influences. Adapted from [4].
relation to human health and comfort; the probability of perception Factors that contribute to the onset of motion sickness
of vibrations; manifestation of motion sickness (travel disorders). symptoms can vary such as air quality, odour, temperature, taste,
ISO 2631-1 defines methods for measuring periodic, random and vibration, visual contribution, oxygen ions, stress, sound, head
transient vibrations of the whole body. This section identifies the position, and body posture [19]. The symptoms of motion sickness
main factors that are combined to determine the extent to which the increase with increased exposure to lateral acceleration at low
impact of vibration is acceptable. The frequency ranges considered frequencies (<0.5 Hz) and mainly on predominantly curvy cross-
are from 0.5 Hz to 80 Hz for health, comfort and perception and country routes [15]. In [20] the authors conducted a road
from 0.1 Hz to 0.5 Hz for motion sickness [12]. Low frequency experiment on a fixed suburban route. During the journey, the
acceleration can cause discomfort, instability and motion sickness, spectra of fore-and-aft and lateral acceleration are similar in the
leading to impaired travel comfort. frequency range 0.1–0.5 Hz and consequently the motion sickness
dose values are similar along these axes. At frequencies less than
3. Motion Sickness 0.1 Hz, the fore-and-aft acceleration is slightly greater than the
lateral acceleration. According to the authors, the low-frequency
The term “motion sickness” was first introduced by Irwin in the
publication [13]. He suggests that the term motion sickness is more fore-and-aft and lateral acceleration in cars are more dependent on
the driver's behaviours. After a road experiment, the authors
correct than sea-sickness because “not only does it occur on lakes
conclude that the dose of the sickness for fore-and-aft and lateral
and even on rivers, but as is well known, a sickness identical in kind
acceleration is significantly higher than motion sickness dose values
may be induced by various other motions than that of turbulent
for vertical acceleration.
water,…”. Motion sickness is a response to real or apparent
movement to which human being is not adapted. According to [14] The main factors that cause motion sickness are shown in Fig.
2. According to some studies [16, 17, 21] women are more sensitive
motion sickness is a misnomer for this response, the symptoms can
be caused both by the absence of expected movement and by the than men, the most vulnerable to the symptoms of motion sickness
are children. However, the age group 4 to 12 years is not included
presence of unexpected movement (examples of this are sickness
associated with wide-screen movies and simulators). in the standardized dynamic vehicle tests in either regulatory or
consumer assessment programs [22].
Motion sickness occurs when there is a contradiction between
the perceptions of movement coming from the eyes and the
vestibular apparatus, i.e., a person sees that he is moving but does
not feel it, or vice versa – he feels that he is moving but does not see
it. The vestibular apparatus consists of two main parts – an organ
responsible for the perception and reflection of angular
accelerations and an organ responsible for the perception and
reflection of rectilinear accelerations and gravity. The assessment of
the change in the position of the human body in space also depends
on the change in the position of the eyeball, the musculoskeletal
system, the skin tissue, the constituent ligaments, etc. (Fig. 1). An
example of a contradiction between the perceptions of movement
coming from the eyes and the vestibular apparatus is when reading Fig. 2 The main factors that cause motion sickness. Adapted from [19].
in a car when it is dark outside; the vestibular system then gives
signals for movement, but the visual system does not confirm this The vestibular system is what helps us keep our balance. It
movement and these contradictory factors can cause motion registers changes in position caused by motion and controls the
sickness [15]. Another example of a conflict between the position of the head through regulation of muscle tension which
perceptions of movement and the vestibular apparatus is with a helps us keep our posture. The vestibular system is affected by
person parking a car in a parking lot and the one next to him left. vertical and horizontal vibrations and forces of acceleration [19]
Another such situation can occur when a driver/passenger in a car is that results in motion sickness and ride discomfort (Fig. 3).
waiting at a traffic light and the stopped bus in the next lane set off.
Motion sickness occurs when traveling by car, bus, train, plane
(mismatch between visual and vestibular irritation), sailing (unusual
complexes of linear and angular acceleration with a slow frequency
– less than 1 Hz), use of a simulator, when flying in weightlessness,
as well as when using virtual reality, computer games, etc. [16–18].
According to [17] motion sickness is a general term for many
symptoms and signs, generally unfavourable due to exposure to
abrupt, periodic, or unnatural accelerations. Fig. 3 Vibrations and forces of acceleration that affect the vestibular system
that results in motion sickness and ride discomfort. Adapted from [19].

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Drivers follow the road all the time, do not keep their eyes on In [34] is studied the effect of vehicle vibration on humans. The
stationary objects for a long time and they do not exhibit symptoms calculations are made using a simulation program using a full
of motion sickness. One reason for this may be that the driver can vehicle model with a driver and the results are evaluated using the
predict the direction of the vehicle and therefore aligns his/her head international standard ISO 2631. Road irregularities are chosen as
with the GIF (Gravito Inertial-Force) [19]. The known fact that the impact. The physical model of the studied system is formed by a
drivers rarely become motion sick may be due to the driver’s full vehicle model and a driver. The conclusions made by the
prediction of low-frequency horizontal accelerations as they depend authors after the study: if the driver travels at a speed of 72 km/h
on the driver’s behaviour [23]. Thus, the conflict between the visual from 5 to 6 hours on a smooth road, at frequency ranges from 8 to
perceptions and the sensations of the vestibular apparatus in the 10 Hz he/she feels uncomfortable and should not be exposed to
driver is less pronounced than in the passengers. With the advent of vibration more than 5 hours under these conditions.
autonomous cars, the driver changes his/her role and becomes a In the publication of M. Brogioli at all [35] a mechanical model
passenger. As a passenger, he/she may also at some point show of a seated passenger is presented and through its validation an
symptoms of motion sickness due to lack of vehicle control in analysis of the key parameters that affect ride comfort is performed.
addition to sensory conflicts [24]. In a conflict situation, he/she According to the authors, the size and weight (percentile) of the
probably will not be able to take control of the car. In recent years, human object are crucial for assessing ride comfort. Another
the possibility of autonomous cars entering has increased, and in important component is the seat and its parameters – stiffness,
this connection, consideration should be given to reducing the damping and geometric parameters.
mechanical effects that cause the symptoms of motion sickness. In [30] the influence of vibration frequency and pitch motion
and roll motion on motion sickness are studied using a vibrating test
4. Methods for Measurement the Ride Comfort bench. The conclusions of the experiment are that vertical
vibrations and pitch motion at 0.5 Hz or lower affect the frequency
There are various methods for assessing the ride comfort. In of the sickness when the vehicle is moving. The authors present a
most cases, the acceleration, the frequency of oscillations, the formula that can be used to assess the level of motion sickness,
vibrations, the noise to which the passengers in the land vehicles are using differences in vibration levels and coefficients of influence of
exposed are measured with the help of equipment. The obtained the direction and frequency of vibrations on motion sickness. Road
results are compared with the existing international standards. tests have been carried out with many vehicles to confirm that the
Various factors can affect a person's response to vibrations such as level of motion sickness assessed using the developed formula is in
gender, height, health, driver or passenger etc. Some researchers use good agreement with the result of the subjective assessment. The
methods such as conducting interviews with a lot of participants of methods proposed by the authors are applied to verify the
different age groups, gender, nationality, etc. The comfort that effectiveness of an improved suspension system, which is installed
people feel can be classified as a subjective assessment, as it is in vehicles and suppresses low-frequency vibrations.
possible to detect significant variations in the responses of different
people to the same situation [25]. Mathematical models and 5. Suggestions for Improving the Ride Comfort
computer simulations are used to obtain results, which can
subsequently be compared with results obtained in road experiments Most research and development to improve ride comfort relates
[26–29]. Various vibration measuring test bench are also used in the to ride comfort at frequencies greater than 1 Hz, where movement
laboratory [30] and simulators of driving conditions [31]. The main depends on the dynamic response of the car's suspension and seat.
value for the magnitude of the vibration is the acceleration. At these frequencies, in addition to the suspension and the seat
Accelerometers are used to measure the accelerations to which that serve as isolation from the road, the characteristics of the tires
passengers are exposed when traveling in road vehicles, which also influence, as at frequencies up to 30 Hz the comfort depends on
record the accelerations on all three axes of movement (Fig. 4). In the pressure in them and over 30 Hz on the tire design [36, 37].
some cases, the accelerations are measured only in single axis, for Other sources of high frequency vibrations are the engine and
example if the researchers work on improving the design of the transmission. Elastic engine mounts and drive shaft bushes are used
suspension they are mostly interested in vertical accelerations; if to dampen their vibrations [38]. Dynamic vibration absorbers and
they are working on active transverse stabilizers or tilting systems, crankshaft dampers is widely used in most vehicle engines [39].
they are mostly interested in a change in the lateral accelerations Modern engines with a small number of cylinders and high power
[32]. In [33] the authors explore the possibility of using often use a dual flywheel [40].
smartphones to measure comfort when traveling on trains. They Vehicle movements at frequencies less than about 1 Hz result from
conclude that the accelerometers found in modern smartphones are the road surface profile (for vertical vibrations), cornering (for lateral
of sufficient quality to be used in assessing ride comfort. acceleration) and acceleration and braking (for fore-and-aft
movements). All three are affected by the speed of the vehicle and
differently by the behavior of the driver. In newer suspension designs,
mainly for high class vehicles, active or semi-active suspensions are
used which can reduce roll and pitch angle in this case.

Fig. 4 Accelerometer and DAQ devise used for data acquisition [32].

To predict the onset of motion sickness symptoms, the authors

of [31], studied the effect of lateral oscillations at frequencies
between 0.0315 and 0.2 Hz. The experiment was performed using a
simulator capable of a horizontal displacement of 12 m and
simulating six motion conditions. After conducting an experiment
with 120 people, the authors summarize that there is a very
significant effect of the frequency of lateral vibrations on the Fig. 5 Posture Control Device [28].
appearance of mild nausea.

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Some studies have shown that by tilting the head to the center 7. ISO 5349-1:2001 Mechanical vibration – Measurement and
of the corner, following the example of the driver, the symptoms of evaluation of human exposure to hand-transmitted vibration – Part 1:
motion sickness in car passengers can be significantly reduced, General requirements
leading to improved ride comfort [28, 41–43]. In [28] is present 8. ISO 5349-2: 2001/Amd 1:2015 Mechanical vibration –
posture control device when traveling by car (Fig. 5). The proposed Measurement and evaluation of human exposure to hand-
device has the effect of increasing the stability of the posture and transmitted vibration – Part 2: Practical guidance for measurement
increasing the comfort of passengers when driving in a corner. at the workplace – Amendment 1
In [44] experimental results performed with a tilting vehicle that 9. ISO 10326-1:2016 Mechanical vibration – Laboratory method
was developed by modifying a small electric vehicle are presented. for evaluating vehicle seat vibration – Part 1: Basic requirements
The driver's seat is fixed to the cab, which is attached to the chassis 10. ISO 10326-2:2001 Mechanical vibration – Laboratory method for
of the vehicle and their relative movement is about the axis of evaluating vehicle seat vibration – Part 2: Application to railway vehicles
rotation. An electric motor is attached to one end of the axis of 11. BS EN 12299:2009 Railway applications. Ride comfort for
rotation to simulate a spring and a shock absorber. The tilting passengers. Measurement and evaluation
movement of the cab is mainly based on the lateral acceleration of 12. ISO 2631-1:1997 Mechanical vibration and shock – Evaluation of
the chassis. The tilt angle is limited to approximately 20º (0.35 rad) human exposure to whole-body vibration – Part 1: General requirements
with a mechanical stopper. The results show that the tilting function 13. J. A. Irwin, M. A. Cantab, M. D. Dub and C., The pathology of
significantly reduces the severity of motion sickness and increases sea-sickness, The Lancet, 118(3039), pp. 907–909 (1881)
ride comfort. 14. T. G. Dobie, Motion Sickness. A Motion Adaptation Syndrome,
Tilting the chassis, following the example of railway transport, Springer, p. 302 (2019)
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