Car SAfety

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1. INTRODUCTION
The death toll on the world roadways make driving the number one cause of
death and injury for young people aging from 15 to 44 which kills more than one
million people a year and injuring another thirty eight million seriously. Cars are
getting must safer in recent years because safety is the selling point in new cars--
people actually seek out and buy safer cars. With the introduction of airbags, crash
testing and other smart equipments in the vehicles, the number of people killed and
injured by motor vehicles has decreased in many countries.
Prior to the mid-1960s, the role of vehicle design in preventing crashes and
mitigating crash injuries was not generally considered. The focus at that time was on
trying to prevent crashes by changing driver behavior (O’Neill, 2003). However, in
1966, in the aftermath of U.S. senate hearings on vehicle safety, legislation was
enacted that authorized the U.S. federal government to set safety standards for new
vehicles. The result, in 1967, was the first U.S. federal Motor Vehicle Safety Standard
specifying requirements for seat belt assemblies. A host of other regulations quickly
ensued to address vehicle performance in several categories: pre-crash (e.g., tires,
brakes, transmissions), crash-phase (e.g., head restraints, front and side impact
protection, roof crush, windshields), and post-crash (e.g., fuel system integrity,
flammability of interior materials).
Shortly thereafter other governments followed suit in implementing similar
regulations, for example, in Europe, Australia, and Canada. Most U.S. motor vehicle
regulations have been evaluated by the National Highway Traffic Safety
Administration (NHTSA) at least once since 1975 (Kahane, 2008). Based on these
evaluations, NHTSA estimates that Federal Motor Vehicle Safety Standards have
saved 284,069 lives between the time of their inception and 2002 (Kahane, 2004).

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2. FUNDAMENTALS OF MOVING OBJECT
Before looking at the specifics, let’s review the knowledge of the laws of motion.
We know that moving objects have momentum. Unless an outside force acts on it, the
object will continue to move at its present speed and direction. If loose objects
(passengers, luggage.etc.) in a car are not restrained, they will continue moving with
the speed at which the car is traveling, even if the car is stopped by collision. When A
car crashes, the force required to stop an object is very great because the car’s
momentum has changed instantly while the passengers has not.
When your body is moving at the speed of 35 mph (56 kph), it has a certain
amount of kinetic energy. After the crash, when you come to a complete stop, you
will have zero kinetic energy. To minimize the risk of injury, the kinetic energy has to
be removed as slowly and evenly as possible. Ideally the car has seat belt pretensions
and force limiters which tighten up the seat belts as soon as the car hits the barrier, but
before the airbag deploys. The seatbelt then absorbs some of the kinetic energy as you
move forward towards the airbag. Milliseconds later the force limiters kick in making
sure the force in the seatbelts doesn’t get too high. Next the air bag deploys and
absorbs some more of the forward motion for protecting you from hitting anything
hard.

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3. CRASH HALL
To prevent motor vehicle crashes and reduce injuries in crashes the Vehicle
Research Center (VRC) was established in the 1992.VRC includes vehicle and
component testing, including fully instrumental crash tests, plus in depth study of
serious, on-the-road crashes. Scrutinizing the outcomes of both control tests and real
collisions gives researchers a better idea of how and why occupants get injured in
crashes. This research, in turn, leads to vehicle designs that reduce injuries.
Fig.3.1 Crash Hall, showing barrier and lighting system.
Inset: Propulsion system.
The crash hall, which accommodates barrier, tests plus vehicle-to-vehicle head on,
frontal offset and front-to-side impacts with both vehicles moving. The front-into-rear
tests also can be conducted. The unique feature of the crash hall’s lighting system is
that, it can provide 750,000 Watts of light without glare.

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4. CRASH TESTING
As the crash test begins the vehicles are slowly accelerated to impact speed, by
means of propulsion system which uses compressed nitrogen to run the hydraulic
motor that, in turn, drive the cables that tow the vehicles. Some of the crash tests
conducted are as follows:
4.1. SIDE IMPACT CRASH TESTING
In crashes with another vehicles, 51% of driver deaths in recent model cars
during 2000-2001 occurred in side impacts up from 31% in1980-1981.Since 1997 the
federal New Car Assessment Programme has included side impacts.
Fig.4.1 Side impact crash testing

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The test configuration resulting from the research is a 31 mph (50 km/h) perpendicular
impact into the driver side of a passenger vehicle. The moving deformable barrier that strikes
the test vehicle weighs 3,300 pounds (1,500 kg) and has a front end shaped to simulate the
typical front end of a pickup or SUV. In each side-struck vehicle are two instrumented SID-
IIs dummies representing a small (5th percentile) female or a 12-year-old adolescent. These
dummies are positioned in the driver seat and the rear seat behind the driver.
With good side impact protection, people should be able to survive crashes of this severity
without serious injuries.
4.2. FRONTALIMPACT CRASH TEST:
The federal New Car Assessment Program, which involves 35 mph crash tests
into a full-width rigid barrier, has been highly successful in providing consumers with
comparative crashworthiness information.
Fig.4.2. Frontal Impact Crash Test

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Crashing the full width of a vehicle into a rigid barrier maximizes energy
absorption so that the integrity of the occupant compartment, or safety cage, can be
maintained in all high-speed crashes. Full-width rigid-barrier tests produce high
occupant compartment decelerations, so they're especially demanding of restraint
systems..
4.3. FRONTALOFFSET CRASHTESTING:
Fig.4.3 Frontal offset crash Test
In offset tests, only one side of a vehicle's front end, not the full width, hits the barrier
so that a smaller area of the structure must manage the crash energy. This means the front end
on the struck side crushes more than in a full-width test, and intrusion into the occupant
compartment is more likely. So they’re demanding of structure.
4.4. SEAT ANCHORAGE TEST
The seats to be tested shall be mounted on the vehicle body for which they are
designed. Fig 1 shows the test set up for the seat anchorage test conducted.
A longitudinal horizontal deceleration of not less than 20 g shall be applied for 30 ms
in the forward direction to the whole shell of the vehicle. At the moment of the impact
the vehicle should run free. The speed on impact shall be between 48.3 km/h and 53.1
km/h.

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Fig.4.4 Seat Anchorage Test
4.5. LUGGAGE RETENSION TEST
This test is mainly intended to test the strength of the seat back in case of a
collision, when the seat back is hit by the luggage kept behind the seat back in
luggage compartment. This is mainly done for rear seats. The test blocks are kept on
the floor of the luggage compartment. The luggage is kept at a distance of 200 mm
away from the rear seat back and 50 mm distance in between two luggages. The
weight of the luggages is 18 kg each as specified in the regulation. On board data
Acquisition system is provided for measuring the data
During the test, the seats must be adjusted to ensure that the locking system
cannot be released by external factors. If the seat back is fitted with a head restraint,
the test must be carried out with the head restraint placed in the highest position. The
test shall be carried out with the seat backs in their normal position of use.
4.6. SEAT BELT ANCHORAGE TEST ON DRIVER AND
CO-DRIVER SEATS
This test was conducted as per ECE (Economic Commission of Europe) on the
front row seat belt anchorage of driver seat by simulating the anchorages located on
the body shell on the rigid fixture.

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The specified load is applied to the respective seat belt anchorages
simultaneously on all driver seat belt anchorages through the ECE specified traction
devices. The wire rope was used for transfer of the load between anchorages and the
traction devices using the same path as with the seat belt.
Fig.4.6. Seat belt anchorage test
The load was applied synchronously using servo hydraulic actuators; a computer
based single controller, which applied synchronous load on all the actuators. Fig
shows the typical Loading cycle for the Seat Belt Anchorage test on driver seat. Load
was applied on driver’s lap and driver’s torso, through the specified traction devices
as shown in Fig shows Seat Belt Anchorage test carried out on Body shell.
The tractive force is applied in a direction corresponding to the seating position at an
angle of 10 5 above the horizontal in a plane parallel to the median longitudinal
plane of the vehicle.
Post inspection is carried on the seat belt anchorages to check any failure or
dangerous deformation during the test.

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5. CRASH TEST DUMMIES
The dummy’s job is to simulate a human being during a crash, while collecting data
that would not be possible to collect from a human occupant.
All crash tests in the United States are conducted using the same type of dummy, the
Hybrid III dummy. This guarantees consistent results. A dummy is built from
materials that mimic the physiology of the human body. For example, it has a spine
made from alternating layers of metal discs and rubber pads. The dummies come in
different sizes and they are referred to by percentile and gender.
For example, the fiftieth-percentile male dummy represents the median sized male --
it is bigger than half the male population and smaller than the other half.
TYPES OF DUMMIES
Hybrid III dummies are used for frontal crash testing
Child restraint-airbag interaction dummies representing 6 and 12 month-olds
BioSID and SID-II(s)
5.1. BioRID
A rear-impact dummy has been developed to measure the risk of minor neck injuries,
sometimes called whiplash, in low-speed rear-end crashes -- a big problem
worldwide. BioRID has been designed especially to study the relative motion of the
head and torso. For tests representing crashes in which a vehicle is struck in the rear,
BioRID can help researchers learn more about how seatbacks, head restraints, and
other vehicle characteristics influence the likelihood of whiplash injury. He is
designed to represent a 50th percentile or average-size man, 5 feet 10 inches tall and
170 pounds.

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Fig. 5.1 BioRID
Unlike Hybrid III dummies, BioRID's spine is composed of 24 vertebra-like pieces, so
that in a rear-end crash BioRID interacts with vehicle seats and head restraints in a
more humanlike way than the Hybrid III. Plus BioRID's segmented neck can take on
the same shapes observed in human necks during rear-end collisions, an important
characteristic for measuring some risk factors associated with whiplash injury.
5.2 Child Restraint Air Bag Interaction (CRABI)
The Child Restraint Air Bag Interaction dummy was developed by First
Technology Safety Systems to represent children. It's used to evaluate child restraint
systems, including airbags. There are three sizes: 18 month-old, 12 month-old, and 6
month-old. These dummies have sensors in the head, neck, chest, back, and pelvis that
measure forces and accelerations.
Fig.5.2 CRABI

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5.3. THOR
This advanced 50th percentile male dummy is being developed in the United
States for use in frontal crash tests. THOR has more human-like features than Hybrid
III, including a spine and pelvis that allow the dummy to assume various seating
positions -- slouching, for example, or sitting upright. THOR also has sensors in his
face that measure forces so that the risk of facial injury can be assessed.
Fig.5.3. Thor

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6. SAFETY DEVICES
6.1. Seatbelts
The choice of occupant restraint systems for passenger vehicles has been
changing rapidly with the advent of newer passive restraint systems. But the use of
seatbelts has proven the most effective in of the studies carried out for frontal crashes.
Many injuries to the occupant can be minimized by the use of the seatbelts. One of the
most important aspects of seatbelt is that it should work 100 out of 100 times when
installed in the car.
Even at modest town speeds of 30 mph, striking a rigid object such as a
concrete lamp will cause the car to be brought to rest in a little more than one tenth of
a second over a front end crush distance of 2 feet. An unrestrained occupant will
strike the car interior at almost the initial velocity of the car. The effect of seat belt is
not just to restrain the occupant away from projections, which can impose high-
localized forces, but also to reduce the forces on the whole body. Stretching of the
belt in the impact allows the body to move forward about 8 inches. A resulting
stopping distance of 12 inches for the body could typically be assumed in the 50-km/h
rigid impact situation.
The three-point belt with retractor reel has become almost accepted norm. The
retractor mechanism is such that when a certain vehicle deceleration value is reached
fast response interlock inhibits the webbing roller. Let us first understand the
definitions of seatbelts and its related parts.
Safetybelts: -
An arrangement of straps with a securing buckle, adjusting devices and
attachments which is capable of being anchored to the interior of a power driver
vehicle and is designed to diminish the risk of injury to its wearer, in event of
collision by limiting the mobility of the wearer’s body.

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Belt Anchorage: -
It means the part of the vehicle structure or the seat structure or any other part of
the vehicle to which the safety belt assemblies are to be secured.
6.2. AIR BAGS
Air bags have been under development for many years. The first commercial
air bags appeared in automobiles. Since model year 1998, all new cars have been
required to have air bags on both driver and passenger sides. What an air bag wants to
do is to slow the passenger's speed to zero with little or no damage. The constraints
that it has to work within are huge. The air bag has the space between the passenger
and the steering wheel or dash - board and a fraction of a second to work with. Even
that tiny amount of space and time is valuable, however, if the system can slow the
passenger evenly rather than forcing an abrupt halt to his or her motion.
There are three parts to an air bag that help to accomplish this feat:
The bag itself is made of a thin, nylon fabric, which is folded into the steering
wheel or dashboard or, more recently, the seat or door. The sensor is the device that
tells the bag to inflate. Inflation happens when there is a collision force equal to
running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). A
mechanical switch is flipped when there is a mass shift that closes an electrical
contact, telling the sensors that a crash has occurred. The sensors receive information
from an accelerometer built into a microchip. The air bags' inflation system react
sodium azide (NaN3) with potassium nitrate (KNO3) to produce nitrogen gas. Hot
blasts of the nitrogen inflate the air bag.
The bag then literally bursts from its storage site at up to 200 mph (322 kph) --
faster than the blink of an eye! A second later, the gas quickly dissipates through tiny
holes in the bag, thus deflating the bag so you can move.

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Fig. 6.2 (A)
Fig. 6.2(B)

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Fig 6.2 (C)
The air bag and inflation system stored in the steering wheel
The inflation system uses a solid propellant and an igniter.The whole process happens
in only one-twenty-fifth of a second. The powdery substance released from the air
bag, by the way, is regular cornstarch or talcum powder, which is used by the air bag
manufacturers to keep the bags pliable and lubricated while they're in storage
When is the air bag deployment needed?
Occupant restraint systems are designed to cushion the motion of occupants
when a collision occurs. If an occupant is unrestrained in a collision, he may come
into contact with the steering wheel or other interior structure. In minor collision, an
occupant may be effectively restrained by the seat belts alone and the air bag
deployment may not be needed. In high severity crashes, the potential for serious
injuries to the occupant becomes much greater. Most frontal air bag systems are
deployed when collision occurs with a speed change of 16 km/h or more. Due to the
diversity of crash conditions in the real world and the manufacturing tolerances of
sensors, the deployment threshold will not be precisely fixed at 16 km/h or some other

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value. In fact, the threshold is often set as a range. For unbelted occupants, atypical
threshold zone or range is 13 to 22 km/h.
The threshold range implies that:
No deployment should occur for the impacts with an equivalent collision speed below
the lower limit of the range.
Deployment is expected for impacts with an equivalent collision speed beyond the
higher limit of the range.
Deployment may or may not occur for the situations that fall within the threshold
range.
In all the points that we have seen so far the sensors plays an important role in the deployment
of air bags. Therefore a brief study has to be carried out on sensors.
6.3. SENSORS
Sensors can be placed in different locations on a vehicle. Many vehicles have
one or more sensors located in the front & behind the bumper. Some sensors are
places in the passenger compartment, such as under the dashboard, or on interior
floor. While a vehicle is in collision, the vehicle body experiences strain, deformation,
or fracture. In a minor impact, the front bumper absorbs the energy while still
protecting the engine and the structures behind. In a mild or modest collision, the
front bumper is pushed back by the impacting object and structural changes occur to
the engine compartment. In more severe crashes, the engine itself is forced rearward,
and the frame under the vehicle body undergoes a significant deformation and
fracture.
One essential design requirement of the crash sensors is the ability to
differentiate small impacts from mild and severe crashes the latter of which
necessitate activation of the air bags or other restraint devices. In low speed collision
situation, such as 8kmph vehicle to barrier crashes the sensing systems should not
trigger the bags. In modest collision situations such as 24-32 km/h, the sensing
systems are usually designed to trigger the bags, especially when the passengers are

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not belted. From the onset of the collision, the sensing system will trigger within 10-
20ms.
The functionality of the current sensor system technology has expanded
beyond that of the conventional restraint system. The operation of an integrated
sensing system may compromise the following four stages:
1. Anticipation: -
This first stage involves the pre-impact estimation of upcoming collisions scenarios.
For example, the information from some type of proximity sensor can enhance the
timeliness of the sensor triggering.
2. Confirmation and Discrimination: -
As a collision occurs, the crash sensors are engaged in the process of conforming or
discriminating among the measured signals. In addition to performing the role of
crash detection, crash sensors may be required to the types earlier discussed and the
degree of crashes so that a proper controls command can be executed.
3. Deployment control: -
In this stage, the function of the sensing system is twofold. On one hand, the control
unit must receive inputs from various sensors to establish details about the crash itself
and about the interior of the vehicle, information such as occupant positions. On other
hand, the control unit must command the type of restraint such as air bag and degree
of deployment.
4. Impact Handling: -

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The last stage involves actions that can be taken to mitigate the consequences of an
accident. For example providing communication facilities based on wireless
communication. Thus mounting sensors at the right place can be extremely helpful in
deployment of the air bag in the vehicle interior thus ensuring safety of the occupant.
Some of the sensors are:
1. Accelerometers
These devices measure the acceleration in a particular direction. This data can be used
to determine the probability of injury. Acceleration is the rate at which speed changes.
For e.g. If you bang your head into a brick wall, the speed of your head changes very
quickly (which can hurt!). But if you bang your head into a pillow, the speed of your
head changes more slowly as the pillow crushes (it doesn’t hurt!).
The crash-test dummies have accelerometers all over it. Inside the dummies head,
there is a accelerometer that measures the acceleration in all three directions (fore-aft,
up-down, left-right). There are also accelerometers in the chest, pelvic, legs, feet and
other parts of the body.
Fig.6.3.1 A graph of the head acceleration during a crash test
The graph above shows the acceleration of the drivers head during a 35mph frontal
crash. Notice that it is not a steady value, but fluctuates up and down during the cash.

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This reflects the way the head slows down during a crash, with the highest value
coming when the head strikes hard objects or the air bag.
2. Load sensors
Inside the dummy are the load sensors that measure the amount of force on different
body parts during a crash.
Fig. 6.3.2 The graph of the force in the driver’s femur during a crash
The graph above shows the force in Newton’s in the drivers femur (the thigh bone),
during a 35mph frontal crash. The maximum load in the bone can be used to
determine the probability of it breaking.
Fig. 6.3.3 the chest deflection during a 35-mph frontal impact
3. Movement sensors

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These sensors are used in the dummy’s chest. They measure how much the chest
deflects during a crash. The graph above shows the driver’s chest deflection during a
crash. In this particular crash, the driver’s chest is compressed above 2 inches
(46mm). This injury would be painful but probably not fatal.
7. FUTURE SAFTY IMPROVEMENTS
7.1. DrowsyDriver Monitoring:
APL is developing a small sensor system that will alert drivers when they are in
danger of falling asleep at the wheel or experiencing some level of impairment from
fatigue. The Drowsy Driver Detection System is a device containing a transceiver
similar to those used in automatic door entry systems, which operate at safe
microwave frequency and power levels.
7.2. CollisionWarning Systems
APL is participating in a multi-year program funded by the National Highway Traffic
Safety Administration (NHTSA) to develop a vehicle collision warning system. The
APL-developed software will process input data received from a vehicle-mounted
radar and other vehicle subsystems in real time and generate appropriate warning
signals to alert drivers and help them avoid rear-end collisions.
7.3. Automated CollisionNotification
Another program at APL, focuses on improving highway safety by reducing the time
required for emergency medical units to respond to crash scenes.
7.4. Smart Airbags

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Eventually, we will see smart air bags that can deploy with different speeds and
pressures depending on the weight and sitting position of the occupant, and also on
the intensity of the crash.
7.5. Improved SeatBelts
We’ll see seat belts that will also sense the weight and position of the occupants and
adjust the tension and maximum force accordingly.

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8. PRECAUTIONS TO AVOID SERIOUS INJURY
DURING A CRASH
WearSeatBelts
Regardless of vehicle choice, the consumer and his or her passengers can dramatically
reduce their risk of being killed or seriously injured in a rollover crash by simply
using their seat belts. Seat belt use has an even greater effect on reducing the
deadliness of rollover crashes than on other crashes because so many victims of
rollover crashes die as a result of being partially or completely thrown from the
vehicle. NHTSA estimates that belted occupants are about 75% less likely to be killed
in a rollover crash than unbelted occupants.
Avoid Conditions That Lead To Loss of Control
Common reason why drivers lose control of their vehicles and run off of the road
include: driving under the influence of alcohol or drugs, driving while sleepy or
inattentive, or driving too fast.
Be Careful on Rural Roads
Drivers should be particularly cautious on curved rural roads and maintain a safe speed to
avoid running off the road and striking a ditch or embankment and rolling over.
Avoid Extreme Panic-like Steering
Another condition which may cause a rollover is where a driver overcorrects the
steering as a panic reaction to an emergency or to something as simple as dropping a
wheel off the pavement. Especially at freeway speeds, over correcting or excessive

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steering may cause the driver to lose control resulting in the vehicle sliding sideways
and rolling over. If your vehicle should go off the roadway, gradually reduce the
vehicle speed.
9. CONCLUSIONS
What can be inferred from the studies is that research and development efforts
towards occupant restraint systems have moved in the direction of integrated or
complete system design. Design of complete system not only considers the necessary
components but also uses full advantages of all components. We can see that use of
seatbelts and air bags when combined together provides the best protection. The
extensive test procedures led down really establishes a certain seat or seatbelt and can
guarantee minimum injury to the occupant.
The design of occupant protection can be viewed as an “energy management”
issue. During a collision, the restraint system responds to “manage” the kinetic energy
of the occupant. The objectives are to dissipate this energy as smoothly as possible so
that occupant injuries can be avoided or minimized. The forces on the occupant
should be low and the excursion of the occupant limited. A poorly designed restraint
may impose extreme forces on the occupant or allow excessive excursion of the
occupant.
Energy management can be extended to the component level as well. The
design of inflators is a perfect example. Inflators are required to be powerful and fast
because the time frame for their functioning sequence is very limited; consequently,
the speed of deployment and the level of released energy are high.

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10. REFERENCES
1.’ IEEE TRANSACTIONS ON INTELLIGENT TRANSPORTATION
SYSTEMS’, Vol. 8, NO. 1, MARCH 2007.
2. ‘IEEE TRANSACTIONS ON INTELLIGENT TRANSPORTATION SYTEMS’,
VOL. 4, NO. 3, SEPTEMBER 2003.
3. ‘Safety in Semi-autonomous Multi-vehicle systems: A Hybrid Control Approach’
by Rajeev Verma, Member, IEEE, Domitilla Del Vecchio, Member, IEEE,
NOVEMBER 2009.
4. ‘ACCIDENT AVOIDANCE AND DETECTION ON HIGHWAYS’ International
Journal of Engineering Trends and Technology- Volume3Issue2- 2012.
5. ‘Technical feasibility of Advanced Driver Assistance Systems (ADAS) for road
traffic safety. Transportation Planning and Technology’, vol. 28 issue 3 pp 167-187.
6. http://www.howstuffworks.com/howairbagswork.htm
7. http://www.howstuffworks.com/howcrashtestingworks.htm
8. http://www.hwysafety.org/vehicle-ratings/vrc2.html
9. http://www.google.com/crashtestdummies.htm
10. http://www.cnse.Caltech.edu/research/reports/zhang-ull.html
11. http://www.viewz.com/featurearticles/smartcar.html