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Car safety systems are technologies within cars designed to work such that they reduce the occurrence of road
accidents and minimise the consequences if road accidents do occur. Car safety systems can be categorised into two
main categories:
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active systems
passive systems
An active safety system is one which assists in the prevention of the accident whilst passive systems are features of
the vehicle which give some form of protection to the passengers of the vehicle.
This website contains information about active safety systems and in particular those which assist the driver in
detecting potential hazards and avoiding them often through the system taking control of the vehicle to avoid
collision.
Driver assisting active safety systems include:
 Lane departure warning
 Traction Control
 Automated Parking
 Reversing sensors
 Anti-lock braking
 Adaptive cruise control
Amongst others
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Infrared night vision
Tyre pressure monitoring
Adaptive headlights
Electronic stability control
Cornering Brake control
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Adaptive Cruise Control
Adaptive cruise control (ACC)is very much like a standard cruise control system on a car but with the added
dimension that it uses radar or other sensors to measure the distance between the vehicle in front and the vehicle
the system is in.
This enables the ACC to operate with two functions; speed control and spacing control. When the car has no vehicles
in front of it then the system operates as a standard cruise control system by maintaining a speed set by the driver
(speed control); however if the ACC enabled car does have a vehicle preceding it on the road, the radar will detect
the other vehicle and calculate the distance between the vehicles, from this information the ACC system will then
determine if it is safe to continue traveling at the driver – set speed or not. If the preceding vehicle is too close or is
travelling with a low speed then the ACC system operates in spacing control mode, in which the throttle and brakes
are automatically controlled to keep a desired safe distance from the vehicle in front (Rajamani, 2012)
ACC acts as both a safety feature and also as a improvement for driver comfort and convenience; by relieving the
driver from the duty of maintain good spacing from preceding vehicles when travelling at motorway speeds, which is
how the systems are marketed. Some manufactures of luxury cars including BMW have started the implementations
of such systems.
Of all American highway accidents over 90% of road accidents are due to human error rather that equipment or
conditions (US Department of Transportation, 1992, cited by Rajamani, 2012), which is where ACC can act as a safety
feature. An ACC system is constantly measuring the distance to preceding vehicles and calculating the required
actions using control algorithms thus if a preceding vehicle brakes suddenly and the distance decreases the ACC
system will react to this change faster than a human driver and so should reduce the number of collisions especially
rear end collisions of which there are 1.8 million annually (Vahidi, 2003).
Standard ACC works only for motorway style driving, most testing of ACC systems is conducted at speeds greater
than 40 km/h. Stop and Go cruise systems are also under development and are designed for traffic conditions more
like city driving. In such systems the ACC is able to accelerate and decelerate much more so than a standard ACC
system.
In Liang and Peng’s (2000) ‘String stability analysis of adaptive cruise controlled
Vehicles’ they found that in traffic in which vehicles are equipped with ACC the average velocity is greater and
average acceleration is lower. This therefore is likely to mean that the amount of congestion can be reduced, fuel
consumption can be lowered and smoother driving achieved. On similar lines studies by Bose and Loannou (2001)
showed that air pollution can be reduced.
For ACC systems to work effectively however they must be understood by the drivers of the vehicles. Goodrich et al.
(1999) proposed that the following four factors need to be established for an ACC system to be safe for operation.
1.
2.
3.
4.
The way the ACC systems acts must be predictable
The switching of control between the ACC and the driver must be fluid and undetectable
The limits of the ACC system must be obvious to the driver
The decrease in workload should not lead to the driver having excess attention based responsibilities and
decision making.
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Electronic Stability Control:
A Vehicle stability control system often referred to as Electronic Stability Control (ESC) is designed to detect a loss of
vehicle stability, through a loss of traction; and act to correct it, to prevent spinning or drifting of the vehicle.
1987 saw the invention of the first ESC by Mercedes-benz and BMW, since then ESC has been used by many vehicle
manufactures as a safety feature including, Saab, Opel, Ford, Holden and GM who were some of the earliest
manufactures to introduce the systems. In 2008 the European Commission confirmed a new proposal for the
mandatory introduction of ESC on all new cars sold in the EU from 2012, with all new cars being equipped by 2014.
There are three typs of ESC in use or under research and development:
1. Differential Braking – the use of an ABS brake system to apply different braking to the left and right wheels
2. Steer-by-wire – use of the driver’s steering angle and a correction input to create a better steering angle for
the wheels
3. Active Torque Distribution – the use of independent control of the amount of drive torque distributed to
each wheel
Differential Braking and Steer-by-Wire are more commonly used than Active Torque Distributions systems.
Differential braking systems use hydraulics to change the brake pressure at each wheel. Increasing the brake
pressure at the outer front wheel would counter oversteer whilst increasing pressure at the inner rear wheel would
help minimise understeer due to the clockwise and anti-clockwise moments that would be created. Increasing
pressure to the left wheels would cause of clockwise moment.
With a steer-by-wire systems the angle of the steering at the front wheels is altered to minimise the effects of losing
traction. The angle at which the front wheels steer is made up of two factors. Firstly the input from the driver as
determined by the movement of the steering wheel, secondly a input decided by the steer-by-wire computerised
system to alter the driver determined steering to prevent skidding. The second component however must not alter
the vehicle path chosen by the driver.
Active Torque Distribution systems works by delivering drive torque to the wheels independently so different wheels
receive different levels of torque. The advantage of using a drive torque control system rather than a differential
braking system is that with the drive torque control system the vehicle does not decelerate during the use of the
ESC.
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Intelligent Speed Adaptation:
Intelligent Speed Adaptation (ISA) systems constantly checks both the vehicle speed and the local speed limit and
then takes action if the vehicle speed is greater than the speed limit.
ISA systems consist of three parts, a receiver (usually GPS), a computer and a display unit which shows the permitted
speed limit and warning signals.
There are currently two types of ISA passive, also known as advisory, and active, also known as full. Passive systems
give warnings to the driver when the vehicle exceeds the speed limit, these warnings can be audio or visual or in
some more advanced systems the accelerator pedal is affected by either becoming stiffer or vibrating. With active
systems, the system is able to reduce the vehicles speed without any driver input, again there are various methods
including include throttle control, brake application, engine management system manipulation, fuel limiting or a
combination of these (Zoghi et al.). Most active ISA systems also have an override so that the driver can stop the ISA
system is needed.
In order for ISA systems to work the system must know the location and speed of the vehicle at all times. There are
multiple ways in which the ISA system can determine the location of the vehicle and thus the local speed limits. The
information about the location must also be linked to an extensive database or map of information of speed limits
including variable speed limit zones so the system can determine whether the vehicle is speeding. The most
common ways are as follows (Zoghi et al.):
1. Global Positioning System (GPS) – a series of satellites constantly transmit radio signals that are detected by
GPS receivers. By using the signals from 4 or more satellites a precise 3 dimensional position can be found.
2. Radio Beacons – In car receivers pick up signals each time they travel past a radio beacon positioned at the
side of the road or on road signs etc which transmit radio signals constantly. The radio beacons would also
be able to transmit other information such as weather warnings. It would also be possible to have mobile
beacons taking precedence over static beacons that give temporary information, for example at crash sites.
3. Dead Reckoning (DR) – a mechanical system linked to the driving assembly able to track by prediction the
vehicles path by measuring different parameters such as steering wheel angle. However knowledge of a
fixed start location is needed and this system looses accuracy over time making the system unreliable on its
own. It works best when used in conjunction with other systems for example when a GPS systems fails in a
tunnel a DR system would be able to continue tracing the vehicles path.
It is possible that advanced ISA will be able to receive real time data and update information as situations change
such as road works or bad weather conditions. It is also possible that ISA may be able to have knowledge of features
such as sharp bends or road signs for example stop signs.
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References:
VAHIDI, A., 2003. Research advances in intelligent collisions avoidance and adaptive cruise control. Intelligent
Transportation Systems. 4(3), 143-153. ISSN : 1524-9050
MARSDEN, G. MCDONALD,M. BRACKSTONE,M. 2001. Towards an understanding of adaptive cruise control.
Transportation Research Part C: Emerging Technologies. 9 (1), 33-51.
RAJAMANI, R., 2012. Vehicle Dynamics and Control. Boston, MA : Springer US. ISBN 9781461414339
GOODRICH, M. A., BOER, E. R., & INOUE, H. 1999. A model of human brake initiation behaviour with implications for
ACC design. Intelligent Transportation Systems, 1999. Proceedings. 1999 IEEE/IEEJ/JSAI International Conference. 8691
LIANG,C. PENG, H. 2000. String stability analysis of adaptive cruise controlled
Vehicles. Michigan: Michigan University. Available from: http://www-personal.umich.edu/~hpeng/JSME2000.pdf
BOSE, A. IOANNOU, P. Evalusation of the Environmental Effects of Intelligent Cruise Control Vehicles. Transportation
Research Record: Journal of the Transportation Research Board. 1774 90 – 97. ISSN 0361-1981
FARMER, C. 2004. Effect of electronic stability control on automobile crash risk. Traffic injury prevention. 5 (4), 317 –
325. ISSN 1538-9588
ZOGHI, M. HAJALI, M. DIRIN,M. MALEKAN, 2012.Evaluation of passive and active Intelligent Speed Adaption system.
Computer and Automation Engineering. (4), 182-186. ISBN 978-1-4244-5585-0