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Natural Laws and Vehicle Control 5.3 5.4
Driver Education
Legacy High School
2
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.
3
• 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.
4
• Applying pressure to the brake – EXECUTE -- is the braking distance – the slowing and stopping of the vehicle.
5
If you identify a high risk situation, one of the most important things you can do is
decrease speed.
6
Stopping distance
• Braking distance (EXECUTE)
• Reaction time – distance (DECIDE)
• Perception time – distance (IDENTIFY -- PREDICT)
7
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.
8
• 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
9
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.
11
• 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.
13
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.
14
Air bags
• Drivers must have 10-12 inches between their chest and the steering wheel.
15
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
16
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.
17
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.
18
Child seats
• Child seats should be installed in the back seat where air bag deployment will not force the child seat to move.
19
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
21
Safety Glass
• Vehicles are equipped with “safety glass”– Does not break easily.– Does not “splinter” or
have sharp edges.– Breaks into small
pieces.