Next to the driver's attention and skill behind the wheel, the most important aspects of motoring safety are a vehicle's accident-avoidance features. These
are sometimes referred to as "active safety" features because, in simple terms, they "actively" help the driver avoid an accident.
Active car safety features
Active safety features are designed to help the driver retain control of the vehicle when he or she might otherwise lose control. Slippery winter
conditions, winding mountain roads or sudden traffic jams on the freeway are all typical scenarios in which active car safety features can help the driver.
Several important active car safety features became popular on higher-end vehicles beginning in the late 1980s and have since become more mainstream. Here
are the key active safety features on many of today's vehicles.
Anti-lock braking system
What ABS does:
Anti-lock braking systems (ABS) are designed to keep wheels from locking up during hard braking or during normal braking on slippery surfaces. First and
foremost, this helps the driver retain steering control, and in some situations, ABS can also help shorten stopping distances.
How ABS works:
A microprocessor or control unit continually compares the rotational speed of the wheels via electronic sensors located at each wheel. During braking, if
the control unit determines that one of the wheels has locked up, it directs an ABS hydraulic system to individually and rapidly "pump" that brake until
its rotational speed is back in line with the other wheels.
What ABS feels like:
The feel of ABS actuation varies from vehicle to vehicle, but it typically is felt through a pulsing action through the brake pedal, and may include the
sound of the hydraulic pump working. This is normal, and the driver should maintain steady pressure on the brake pedal (without "pumping" the pedal) until
the vehicle has slowed sufficiently to be out of danger.
How ABS benefits the driver:
ABS can help the driver avoid an accident by enabling him or her to steer out of trouble in an emergency-braking maneuver or maintain directional control
during normal braking on a slippery surface.
Electronic brake-force distribution
What electronic brake-force distribution does:
Included in some ABS, electronic brake-force distribution (EBD) electronically distributes the brake hydraulic pressure between front and rear wheels
depending on vehicle load and driving conditions.
How EBD works:
EBD monitors the load on the front and rear axles, and then via the ABS controller sends more braking power to the axle with the greater load.
What EBD feels like:
EBD functions unnoticeably, so the driver is unaware of its operation.
How EBD benefits the driver:
EBD helps ensure that the front and rear tires share the braking loads more effectively under all conditions, which results in better braking performance.
What brake assist does:
Brake assist is included in some ABS and helps the driver apply brakes more fully in an emergency-braking situation.
How brake assist works:
In an emergency, when the driver steps suddenly and forcefully on the brake pedal, brake assist aids in the application of the brakes to help ensure the
shortest possible stops.
What brake assist feels like:
Most drivers won't specifically notice brake assist in operation, though they might detect strong braking performance in "panic stop" situations.
How brake assist benefits the driver:
Brake assist makes the most of the vehicle's braking capability in emergency braking situations, which can shorten stopping distance.
What traction control does:
Traction control is an electronic system that automatically keeps the drive wheels (either front, rear or both in the case of an all-wheel-drive or
four-wheel-drive vehicle) from spinning during acceleration. This improves traction and vehicle stability in slippery driving conditions. (It’s also known
as electronic traction control.)
How traction control works:
A microprocessor compares rotational speeds of the vehicle's front and rear wheels while also tracking such values as throttle opening. When one of the
drive wheels loses traction, its rotational speed quickly rises compared to that of the other wheels. When this happens, the electronic control unit
signals the engine to reduce power output and/or rapidly pulses the brake for the wheel that is spinning. The brake pulsing is done via the anti-lock
braking system hydraulic pump. All cars that have traction control also have ABS (see above).
What traction control feels like:
Traction control activation can differ from vehicle to vehicle. When the system activates, there is generally a momentary delay in acceleration as the
spinning wheel is brought under control. Then the vehicle smoothly accelerates ahead.
How traction control benefits the driver:
The most important benefit of traction control is that it helps the driver retain control while accelerating on slippery surfaces like snow, ice or water –
or even dirt roads or trails. It can also help high-powered cars maintain traction in a straight line or while accelerating on roads that have rough or
Vehicle stability control
What vehicle stability control does:
Vehicle stability control (VSC) is a computer-controlled system that helps the driver retain control of the vehicle during extreme cornering or in other
How VSC works:
VSC utilizes technology from ABS and traction control along with accelerometer technology from aerospace studies.
A sophisticated microprocessor compares the rotational speed of the wheels, the throttle position, steering angle "yaw" (turning motion) and other factors
to determine if the vehicle has suddenly lost grip in a corner and begun to "understeer" (when front wheels slip or "plow" straight ahead) or "oversteer"
(when rear wheels slip or "fishtail").
When this happens, the microprocessor sends signals to the brakes and throttle to help bring the car back in line. Engine output may be momentarily
reduced, and one or more wheels may be braked to help restore control.
What VSC feels like:
Depending on the system, VSC may work seamlessly and imperceptibly to lend a helping hand when the driver has attempted to exceed the vehicle's handling
capabilities, or it may be more abrupt, noticeably slowing the vehicle. The best-engineered systems work so quickly and accurately that the driver scarcely
senses they're at work.
How VSC benefits the driver:
VSC is one of the most effective electronic "helping hands" for drivers invented. By making the vehicle's handling more predictable in challenging
situations, VSC can help the driver better maintain control and avoid an accident.
Vehicle dynamics integrated management
What vehicle dynamics integrated management does:
Vehicle dynamics integrated management (VDIM), is a step beyond VSC in technology and performance.
VDIM enhances handling, traction and braking systems that normally react to vehicle driving conditions by anticipating tire slippage before a skid, slide
or wheel spin occurs and making corrections in a smooth, progressive way.
How VDIM works:
VDIM uses an active control strategy that takes its cues from a comprehensive range of sensors involved in vehicle stability control, traction control,
brake assist, anti-lock brakes and electronic throttle control with intelligence (ETC-I).
In addition, three new technologies are employed that are central to the effectiveness of VDIM: electric power steering (EPS), electronically controlled
brakes (ECB) and Toyota’s (Lexus) variable gear ratio steering (VGRS). VDIM integrates all of these elements with powerful proprietary software to help
seamlessly manage the total vehicle dynamic package.
What VDIM feels like:
Tight integration of all dynamic systems makes VDIM imperceptible to the driver. Since VDIM predicts and then works to prevent loss of vehicle control, the
most noticeable characteristic of the system's operation is the vehicle's unusually predictable handling.
How VDIM benefits the driver:
With all of the traction control technologies working together under the VDIM "umbrella," handling smoothness is dramatically enhanced. VDIM also improves
handling and driving pleasure – even in the most challenging conditions.