Automotive safety
When developing new vehicles it is emphasized that the vehicle meets the safety requirements. These requirements are set by valid regulatory acts, but also by customers
needs. In addition, vehicle manufacturers themselves are developing a variety of safety
features that are intended to increase the safety of the vehicle. The main purpose of vehicle
safety is life and health of the vehicle crew, but also other road users (pedestrians, cyclists, other vehicles, etc.). In general, the goal is to minimize the likelihood of an accident
and if this occurs, to ensure protection of health and life. To achieve this goal it is possible
to apply different features that can be called safety of the vehicle.
The term safety of the vehicle means two basic categories of safety: active and passive
safety.
Active safety
It refers to devices and systems that helps to keep the vehicle under control and prevent an accident. These devices are usually automated to help compensate for human error -- the single biggest cause of car accidents.
Classifications of active safety:
1. Driving or travel safety
2. Conditional safety
3. Perceptual safety
4. Operating safety
1. Driving safety
It is the result of a harmonious chassis and suspension design with regard to wheel suspension, springing, steering and braking, and is reflected in optimum dynamic vehicle behavior.
2. Conditional safety
It is affected by psychological state (of the driver), which depends on the comfort, visibility, vibration, noise and climate impacts.
Visibility – the better driver sees surrounding traffic conditions, the lower is the risk of unexpected situations.
Vibration – affects the driver and result as disturbance (into frequency range of 1-25 Hz
stuttering, tremors etc. falls also vibrations).
Noise – is manifested as audible disturbance when driving the vehicle. It can comes from within (engine, gearbox, shafts, axles) or outside (tyres, road and wind noise). Vibration and noise impact the concentration of the driver. Good sound insulation and well-balanced suspension cab reduces the noise levels, therefore can reduce the risk of road accidents.
Climatic conditions are the air temperature, humidity, air flow and air pressure. Pleasant climate in the car keeps the driver in good condition and ready, even during long journeys. Good heating, ventilation and air conditioning are important for supporting
high standards of vehicle safety.
3. Perceptual safety
The level of safety which increases the perceptual security, focuses on lighting equipment, audio warning devices, direct and indirect view of another vehicle.
4. Operating safety
-relaxed driver (driving without stress), as well a high level of driving safety, requires an optimal design for the driver's surroundings with respect to its comfort. Safety and comfort are interlinked in many aspects. Driver who sits comfortably, has a good posture and easy to read, easy to understand and reach ergonomic devices and controls, can better manage and better concentrate on the surrounding traffic conditions.
The driveline also has an important role. A vehicle that provides good management capacity in terms of electronic engine management, or even automatic transmission, puts less stress
on the driver.
Overview of active safety
Passive safety includes all the features and measures in the vehicle that minimize
the consequences of an accident or prevent it. Passive safety is especially important when
the driver cannot actively intervene in the affairs of the road anymore.
Classifications of passive safety:
Fig. presents the risk to pedestrians in event of collisions with passenger cars as a function of impact frequency and seriousness of injury (based on 246 collisions).
Interior(internal) safety
The term "interior safety" covers vehicle measures whose purpose is to minimize the accelerations and forces acting on the vehicle occupants in the event of an accident, to provide sufficient survival space, and to ensure the operability of those vehicle components critical to the removal of passengers from the vehicle after the accident has occurred.
The determining factors for passenger safety are:
Overview of active safety
Deformation behavior of vehicle body
Due to the frequency of frontal collisions, an important role is played by the legally stipulated frontal impact test in which a vehicle is driven at a speed of 48.3 km/h (30 mph) into a rigid barrier which is either perpendicular or inclined at an angle of up to 30° relative to the longitudinal axis of the car.
Because 50 % of all frontal collisions in right-hand traffic primarily involve the left-hand half of the front of the vehicle, manufacturers worldwide conduct left asymmetrical front impact tests on LHD vehicles covering 30-50 % of the vehicle width. Picture shows the Distribution of accidents by type of collision, Symbolized by test methods yielding equal results in a frontal collision, kinetic energy is absorbed through deformation of the bumper, the front of the vehicle, and in severe cases the forward section of the passenger compartment (dash area). Axles, wheels (rims) and the engine limit the deformable length. Adequate deformation lengths and displaceable vehicle aggregates are necessary, however, in order to minimize passenger-compartment acceleration.
Acceleration measurements and evaluations of high-speed films enable deformation behavior to be analyzed precisely. Dummies of various sizes are used to simulate vehicle occupants and provide acceleration figures for head and chest as well as forces acting on thighs. The side impact, as the next most frequent type of accident, places a high risk of injury on the vehicle occupants due to the limited energy absorbing capability of structural components, and the resulting high degree of vehicle interior deformation. The risk of injury is largely influenced by the structural strength of the side of the vehicle (pillar/door joints, top/bottom pillar points), load-carrying capacity of floor cross-members and seats, as well as the design of inside door panels.
In the rear impact test, deformation of the vehicle interior must be minor at most. It should still be possible to open the doors, the edge of the trunk lid should not penetrate the rear window and enter the vehicle interior, and fuel-system integrity must be preserved.
Roof structures are investigated by means of rollover tests and quasi-static car-roof crush tests. In addition, at least one manufacturer subjects his vehicles to the inverted vehicle drop test in order to test the dimensional stability of the roof structure (survival space) under extreme conditions (the vehicle falls from a height of 0.5 m onto the left front corner of its roof).
The main factor for measuring the severity of vehicle-pedestrian impact is the impact speed. In approximately 70% of crashes, the driver braked before the pedestrian was hit. Almost 95% of all pedestrian accidents occurred at an impact speed lower than 60 km/h, as shown in Figure . Pedestrians struck at impact speeds less than 25 km/h usually sustain minor injuries. Serious injuries occur frequently at speeds of 25-55 km/h whilst at speeds greater than 55 km/h pedestrians are most likely to be killed. According to a study, 79% of the pedestrians were in motion, and in 85% of the cases the pedestrians were hit laterally (37% at the right side, 48% left).
The injury frequency of the pedestrian body segments has been investigated since the
1960s in numerous studies by researchers from different countries.
Pedestrian impact responses
The pedestrian responses to vehicle collisions are rather different for various vehicle front shapes. When an adult is struck by a passenger car front, the first contact occurs between the bumper and either the leg or knee-joint area, followed by thigh-to-bonnet edge contact. The lower extremity of the body is accelerated forwards and the upper body is rotated and accelerated relative to the car. Consequently, the pelvis and thorax are impacted by the bonnet edge and top, respectively. The head may hit the bonnet or windscreen at a velocity estimated as a ratio of 0.7-0.9 to the car-travel speed for big-car bonnet impacts and 1.1-1.4 for small-car head-windscreen impacts. Injuries are usually caused by a direct impact to body segments and a force transmission through the body segments.
2.Neck Injury Tolerance
When developing new vehicles it is emphasized that the vehicle meets the safety requirements. These requirements are set by valid regulatory acts, but also by customers
needs. In addition, vehicle manufacturers themselves are developing a variety of safety
features that are intended to increase the safety of the vehicle. The main purpose of vehicle
safety is life and health of the vehicle crew, but also other road users (pedestrians, cyclists, other vehicles, etc.). In general, the goal is to minimize the likelihood of an accident
and if this occurs, to ensure protection of health and life. To achieve this goal it is possible
to apply different features that can be called safety of the vehicle.
The term safety of the vehicle means two basic categories of safety: active and passive
safety.
Active safety
It refers to devices and systems that helps to keep the vehicle under control and prevent an accident. These devices are usually automated to help compensate for human error -- the single biggest cause of car accidents.
Classifications of active safety:
1. Driving or travel safety
2. Conditional safety
3. Perceptual safety
4. Operating safety
1. Driving safety
It is the result of a harmonious chassis and suspension design with regard to wheel suspension, springing, steering and braking, and is reflected in optimum dynamic vehicle behavior.
2. Conditional safety
It is affected by psychological state (of the driver), which depends on the comfort, visibility, vibration, noise and climate impacts.
Visibility – the better driver sees surrounding traffic conditions, the lower is the risk of unexpected situations.
Vibration – affects the driver and result as disturbance (into frequency range of 1-25 Hz
stuttering, tremors etc. falls also vibrations).
Noise – is manifested as audible disturbance when driving the vehicle. It can comes from within (engine, gearbox, shafts, axles) or outside (tyres, road and wind noise). Vibration and noise impact the concentration of the driver. Good sound insulation and well-balanced suspension cab reduces the noise levels, therefore can reduce the risk of road accidents.
Climatic conditions are the air temperature, humidity, air flow and air pressure. Pleasant climate in the car keeps the driver in good condition and ready, even during long journeys. Good heating, ventilation and air conditioning are important for supporting
high standards of vehicle safety.
3. Perceptual safety
The level of safety which increases the perceptual security, focuses on lighting equipment, audio warning devices, direct and indirect view of another vehicle.
4. Operating safety
-relaxed driver (driving without stress), as well a high level of driving safety, requires an optimal design for the driver's surroundings with respect to its comfort. Safety and comfort are interlinked in many aspects. Driver who sits comfortably, has a good posture and easy to read, easy to understand and reach ergonomic devices and controls, can better manage and better concentrate on the surrounding traffic conditions.
The driveline also has an important role. A vehicle that provides good management capacity in terms of electronic engine management, or even automatic transmission, puts less stress
on the driver.
Overview of active safety
- Anti-lock brakes prevent the wheels from locking up when the driver brakes, enabling the driver to steer while braking.
- Traction control systems prevent the wheels from slipping while the car is accelerating.
- Electronic stability control keeps the car under control and on the road.
- Adaptive cruise control-adjust the vehicle speed based on the traffic environment
- Tyre pressure monitoring system monitors the air pressure inside the pneumatic tyres.
- Lane departure warning system warns the driver when the vehicle is moving out of its lane.
- Night vision system extends the perception of the driver beyond the limited reach of headlights
- Blind spot detection system detects other vehicles located to the driver's side and rear.
- Driver monitoring system is to monitor the driver's attentiveness while driving.
- Road sign recognition system notify and warns the driver of enforced restrictions on the road.
- Electronic Brake-force Distribution distributes the electronic brake power
optimally between front and rear axles. - Intelligent suspension – automatically adjusts ride height according to speed and road conditions.
- Warning system- Signaling of opened door, seat belt warning..etc.
Passive safety includes all the features and measures in the vehicle that minimize
the consequences of an accident or prevent it. Passive safety is especially important when
the driver cannot actively intervene in the affairs of the road anymore.
Classifications of passive safety:
- Interior(internal) safety
- Exterior(external) safety
The term "exterior safety" covers all vehicle-related measures which are designed to minimize the severity of injury to pedestrians, cyclists and motorcycle riders struck by the vehicle in an accident.
Those factors which determine exterior safety are
Those factors which determine exterior safety are
- Vehicle body deformation behavior
- External shape of the car body
The primary objective is to design the vehicle such that its exterior design minimizes the consequences of a primary collision (a collision involving persons outside the vehicle and the vehicle itself). The most severe injuries are sustained by passengers who are hit by the front of the vehicle, whereby the course of the accident greatly depends upon body size. The consequences of collisions involving two-wheeled vehicles and passenger cars can only be slightly ameliorated by passenger-car design due to the two-wheeled vehicle's often considerable inherent energy component, its high seat position and the wide dispersion of contact points. Those design features which can be incorporated into the passenger car are, for example:
- Movable front lamps,
- Recessed windshields wipers,
- Recessed drip rails,
- Recessed door handles.
Fig. presents the risk to pedestrians in event of collisions with passenger cars as a function of impact frequency and seriousness of injury (based on 246 collisions).
Interior(internal) safety
The term "interior safety" covers vehicle measures whose purpose is to minimize the accelerations and forces acting on the vehicle occupants in the event of an accident, to provide sufficient survival space, and to ensure the operability of those vehicle components critical to the removal of passengers from the vehicle after the accident has occurred.
The determining factors for passenger safety are:
- Deformation behaviour (vehicle body),
- Passenger-compartment strength, size of the survival space during and after impact,
- Restraint systems,
- Deceleration systems,
- Control systems,
- Deliverance of passengers,
- Fire protection.
Overview of active safety
- Air bags (front, window, side, knee, front to rear passengers) - prevent the collision
of the body, respectively individual body parts of the steering wheel, instrument panel and other interior parts of the vehicle absorb shock and reduce the risk of injury - Seat belts hold passengers in place so that they aren't thrown forward or ejected from the car.
- Rollover bars protect the car's occupants from injury if the vehicle rolls over during an accident.
- Passenger safety cell
- Crumple zones – reducing the impact of the collision while designing their body structure.
- Whiplash protection- backrest prevent the driver and passengers from getting whiplash during a rear-end collision.
- Child safety system-specifically designed seats that protect children from injury or death during collision.
- Belt bags
- Collapsible steering column – in case of an accident it reduces the driver’s risk of hitting the steering wheel.
- FPS (Fire Protection System Safety) – a system which blocks the supply of electricity and fuel in case of an accident, to avoid the risk of fire.
Deformation behavior of vehicle body
Due to the frequency of frontal collisions, an important role is played by the legally stipulated frontal impact test in which a vehicle is driven at a speed of 48.3 km/h (30 mph) into a rigid barrier which is either perpendicular or inclined at an angle of up to 30° relative to the longitudinal axis of the car.
Depending upon vehicle design (body shape, type of drive and engine position), vehicle mass and size, a frontal impact with a barrier at approx. 50 km/h results in permanent deformation in the forward area of 0.4- 0.7 m. Damage to the passenger compartment should be minimized. This concerns primarily dash area (displacement of steering system, instrument panel, pedals, toe-panel intrusion), underbody (lowering or tilting of seats), the side structure (ability to open the doors after an accident).
Acceleration measurements and evaluations of high-speed films enable deformation behavior to be analyzed precisely. Dummies of various sizes are used to simulate vehicle occupants and provide acceleration figures for head and chest as well as forces acting on thighs. The side impact, as the next most frequent type of accident, places a high risk of injury on the vehicle occupants due to the limited energy absorbing capability of structural components, and the resulting high degree of vehicle interior deformation. The risk of injury is largely influenced by the structural strength of the side of the vehicle (pillar/door joints, top/bottom pillar points), load-carrying capacity of floor cross-members and seats, as well as the design of inside door panels.
In the rear impact test, deformation of the vehicle interior must be minor at most. It should still be possible to open the doors, the edge of the trunk lid should not penetrate the rear window and enter the vehicle interior, and fuel-system integrity must be preserved.
Roof structures are investigated by means of rollover tests and quasi-static car-roof crush tests. In addition, at least one manufacturer subjects his vehicles to the inverted vehicle drop test in order to test the dimensional stability of the roof structure (survival space) under extreme conditions (the vehicle falls from a height of 0.5 m onto the left front corner of its roof).
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| Fig. Inverse drop test |
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Fig.Acceleration, speed and distance traveled, of a passenger compartment when impacting a barrier impacting a barrier at 50 km/h.
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Speed and acceleration characteristics of vehicle body:
 |
| Velocity graph for 15 mph barrier test |
 |
| Velocity graph for 20 mph barrier test |
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| Velocity graph for 40 mph barrier test |
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| Velocity graph for 50 mph barrier test |
All the graphs show the reduction in velocity (speed) of passenger compartment on impact. For 15 mph and 20 mph barrier test, we can see that the velocity comes to zero, crosses zero line, stays in the negative region afterwards. Velocity in negative region means that the car is moving in opposite direction (i. e.) after the collision it moves back. But for 40 mph test, the velocity comes close to zero and lies in the positive region. It means that after the impact, the car does not bounce back much, because most of the energy of the crash is taken by deforming the body metal. But in 15 mph and 20 mph tests, as the speed is low, the kinetic energy to deform the body metal is also less and hence the body metal does not deform and stands rigid. So, the car bounces back and velocity is slightly in the negative region.
Pedestrian safety
Pedestrian injuries
The pedestrian kinematics and injuries in vehicle collisions are influenced by the impact
speed, type of vehicle, stiffness and shape of the vehicle front (such as the bumper
height, bonnet height and length, windscreen frame), age and size of the pedestrians,as well as the initial posture of the pedestrian relative to the vehicle front.
Pedestrian injuries
The pedestrian kinematics and injuries in vehicle collisions are influenced by the impact
speed, type of vehicle, stiffness and shape of the vehicle front (such as the bumper
height, bonnet height and length, windscreen frame), age and size of the pedestrians,as well as the initial posture of the pedestrian relative to the vehicle front.
The main factor for measuring the severity of vehicle-pedestrian impact is the impact speed. In approximately 70% of crashes, the driver braked before the pedestrian was hit. Almost 95% of all pedestrian accidents occurred at an impact speed lower than 60 km/h, as shown in Figure . Pedestrians struck at impact speeds less than 25 km/h usually sustain minor injuries. Serious injuries occur frequently at speeds of 25-55 km/h whilst at speeds greater than 55 km/h pedestrians are most likely to be killed. According to a study, 79% of the pedestrians were in motion, and in 85% of the cases the pedestrians were hit laterally (37% at the right side, 48% left).
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| Injury distribution by body segments |
Injury distribution by body segments
The injury frequency of the pedestrian body segments has been investigated since the
1960s in numerous studies by researchers from different countries.
 |
| Distribution of injuries by body regions of pedestrians struck by the front of cars
(N- injury numbers)
|
The pedestrian responses to vehicle collisions are rather different for various vehicle front shapes. When an adult is struck by a passenger car front, the first contact occurs between the bumper and either the leg or knee-joint area, followed by thigh-to-bonnet edge contact. The lower extremity of the body is accelerated forwards and the upper body is rotated and accelerated relative to the car. Consequently, the pelvis and thorax are impacted by the bonnet edge and top, respectively. The head may hit the bonnet or windscreen at a velocity estimated as a ratio of 0.7-0.9 to the car-travel speed for big-car bonnet impacts and 1.1-1.4 for small-car head-windscreen impacts. Injuries are usually caused by a direct impact to body segments and a force transmission through the body segments.
 |
| The representative distribution of the injuries to an adult pedestrian in frontal
car-pedestrian collisions, trajectories of the head with respect to small and big cars,
changes of the locations of the head impact at varying impact speeds and the
wrap-around distance |
hb- bumper height, hp-pedestrian height, he- leading edge height
Pedestrian safety features
- Automatic braking
- Emergency automatic braking
- Advanced infotainment
- Improved headlights
- Modified design of the bonnet
Severity Index
The Acceleration Severity Index (ASI) is used to evaluate the potential risk for occupant in full-scale crash tests involving roadside safety hardware. Despite its widespread use across Europe, there is a lack of research relating this metric to occupant injury in real-world collisions. Recent installation of Event Data Recorders (EDRs) in a number of late model vehicles presents a different perspective on the assessment of the validity of occupant risk based on the Acceleration Severity Index. EDRs are capable of electronically recording data such as vehicle speed, brake status and throttle position just prior to and during an accident.
Using measured vehicle acceleration information, the ASI is computed using the following relationship:
Human Impact Tolerance
This is the area of study in impact bio-mechanics and is closely tied to rule-making as well as the design of dummy instrumentation to ensure that the parameters measured are in the injury range. It is also the most difficult area of study because of the large variation in mechanical properties of human tissue due to age, gender, weight and geometry. All of these factors are in addition to the normal biological variation in tissue strength and the acceptable level of injury.For example, frontal crashes do not cause serious neck problems unless the deceleration is very high. However, minor rear-end collisions can result in long-term neck pain. There are several levels of tolerance. These levels range from the“Ouch” level for volunteer subjects to the LD (Lethal Dose) 50 level at which half of the subjects would suffer a fatality.
To define a reasonably safe level for the average car occupant without having to make the car unaffordably expensive, a moderate to severe level of injury is chosen as the tolerance level. That is, the injuries sustained by the average occupant should not be life threatening. There is an Abbreviated Injury Scale (AIS), developed by emergency room physicians and physicians in other medical specialties to quantify the severity of an injury to each body area. Severity is defined as threat to life and is not based on disability or impairment. On the AIS scale, any injury greater than AIS 4 is life threatening. The severity levels of AIS are explained in Table.
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| abbreviated injury scale |
Determination of Injury thresholds for various Human body parts
1.Head Injury Tolerance
The Head Injury Criterion (HIC) was developed based on the linear acceleration of the skull, impacting a rigid surface. This value may range from 5,000 to over 10,000 rad/s² . The comparison of measured values supplied by the dummies with the permissible limit values as per FMVSS 208 (, chest acceleration: 60 g/3 ms(1 g is the average gravitational acceleration on Earth, the average force, which affects a resting person at sea level. 1 g = 9.80665 m/s² = 32.17405 ft/s²), upper leg force: 10 kN) are only limited in their applicability to the human being.
2.Neck Injury Tolerance
Neck tolerance is defined in terms of the various modes of loading.
- Tolerance of the Neck In flexion-Extension
- Tolerance of the Neck in Extension
- Tolerance of the Neck in Lateral Bending
3.Thoracic Injury Tolerance
Frontal thoracic tolerance can be expressed in terms of acceleration or displacement.
- Frontal Thoracic Tolerance
- Lateral Thoracic Tolerance
The current criteria for frontal impact are either impact force or compression. Since it was difficult to cause injury to abdominal organs, animal data were used as the basis for abdominal injury limits.
- Tolerance of the Abdomen to Frontal Impact
- Tolerance of the Abdomen to Side Impact
Frontal tolerance of the pelvis does not appear to have been measured directly. The injury from lap belt loads, in the absence of an airbag, indicates that pelvic tolerance is relatively high for frontal impact. At present, the accepted criterion is a 10 kN impact force limit for male and 4.6 kN for female.
- Tolerance of the Pelvis to Frontal Impact
- Tolerance of the Pelvis to Lateral Impact
- Tolerance of the Femur
- Tolerance of the Patella
- Tolerance of the Knee
- Tolerance of the Tibia
- Tolerance of the Ankle
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