Natural Laws and Vehicle Control 5.3 5.4

Driver Education

Legacy High School

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Perception time and distance

• The length of time that it takes to Identify, Predict to stop is called perception time.

• The distance the vehicle travels during this time is called the perception distance.

• To help reduce your perception time, look 12 or more seconds down the road and keep a following distance of at least 4-6 seconds.

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• Once a hazard or reason to stop is recognized, the length of time you take to DECIDE is called reaction time.– The average driver’s reaction time is ¾ second.

• The distance the vehicle travels during this time is called reaction distance.

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• Applying pressure to the brake – EXECUTE -- is the braking distance – the slowing and stopping of the vehicle.

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If you identify a high risk situation, one of the most important things you can do is

decrease speed.

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Stopping distance

• Braking distance (EXECUTE)

• Reaction time – distance (DECIDE)

• Perception time – distance (IDENTIFY -- PREDICT)

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Estimating stopping distance

Use the four-second rule which enables you to to predict a stopping distance under ideal conditions.

1. Pick a fixed point • A sign, mark or shadow on the roadway ahead.• Note when the vehicle in front of you passes this point.

2. Count off seconds• One-thousand-one, one-thousand-two ……

3. If you reach the fixed point sooner than one-thousand-four, you need to increase your following distance.

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• Remember, the four second rule only applies to ideal conditions. Increase your following distance when conditions are less than ideal.– Poor weather – rain, ice, snow, dust storms– Poor visibility – night time driving– Poor road conditions – dirt, gravel– Downhill – Heavy loads

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Factors that affect braking distance

• Speed – – Increased speeds mean increased braking

distance.– Double speed, braking distance is 4x as long– Triple speed, braking distance is 3x as long.

• Vehicle condition– Worn tires or shock absorbers increase braking

distance.

• Road surfaces– Wet, snow, dirt, gravel – increase braking

distances.

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Factors that affect braking distance

• Driver ability– Distracted drivers take longer times to IDENTIFY

and PREDICT the need to stop.– Driving under the influence – decreases ability to

IDENTIFY and PREDICT the need to stop.

• Hills– Braking distances are increase when driving

downhill – increase following distances.

• Loads– Double the weight in a vehicle, double the

stopping distance.

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• The force which which a moving object hits another object is call force of impact.

• Three factors control this force– Speed – most important factor in decreasing

force of impact, cut speed in half, force of impact is reduced 4x.

– Weight – Doubling vehicle weight will double the force of impact.

– Stopping distance/time – the distance or time between initial impact and the time the vehicle stops.

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• Vehicles are built to protect occupants– “Crush” or “Crumple”

zones – areas of the vehicle that “crumple” to absorb the energy of an impact.

– Note that the passenger cabin is relatively undamaged.

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Air bags

• Air bags reduce the force of impact between the driver and the windshield and steering column.

• Air bags are meant to be used in combination with seat belts.

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Air bags

• Drivers must have 10-12 inches between their chest and the steering wheel.

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Air bags

• To avoid air bag injury to hands, wrists and arms, keep your hands on the sides of the steering wheel.

• Keep arms away from the center of the steering wheel.

Air Bag Deployment Area

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Side impact air bags

• Side impact air bags are designed to prevent or decrease injuries to vehicle occupants in the event of a collision to the side of the vehicle.

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Seat belts

• Seat belts are made to hold occupants in place during an emergency.

• Apply so that lap portion of the belt touches thighs and is snug.

• Shoulder portion should cross the middle of the chest.

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Child seats

• Child seats should be installed in the back seat where air bag deployment will not force the child seat to move.

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Head restraints

• Head restraints help prevent or reduce neck injuries (whiplash) during rear end collisions.

• Adjust the head restrain to reach the middle of the back of the head.

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Energy absorbing bumpers and cages

• Most vehicles have energy absorbing bumpers and reinforced passenger compartments.

Reinforced doors for side impact protection

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Safety Glass

• Vehicles are equipped with “safety glass”– Does not break easily.– Does not “splinter” or

have sharp edges.– Breaks into small

pieces.