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Drive To Survive > CH 1-5 > Flashcards

CH 1-5 Flashcards

1
Q

Goals of this program
What it’s designed to address

A
  • teach emergency responders that no matter how long they’ve been driving or how “good” they think they are, at some point Mother Nature (physics) will take over and the vehicle will lose control
  • issues specific to DRIVING the vehicle, not OPERATING. Purpose is to “fill in the gaps” related to vehicle dynamics and crash causation
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2
Q

NFPA Standards

A

-NFPA 1002 “Standard for Fire Apparatus Driver/Operator Professional Qualifications-Section 4-3
-NFPA 1451 “Standard for Fire and Emergency Service Vehicle Operations Training Programs”
-NFPA 1500 “Standard on Fire Department Occupational Health and Safety Program” -section 6

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3
Q

Stopping Distance

A

Distance it takes a vehicle to come to a stop

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4
Q

Total Stopping Distance (4 Phases)

A
  1. Perception Distance
  2. Reaction Distance
  3. Mechanical Lag Distance
  4. Braking Distance
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5
Q

Factors of Total Stopping Distance

A

-reaction time
-road conditions
-braking efficiency
-how forcefully brakes are applied
-speed
*account for the time and distance of civilian drive

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6
Q

Perception

A

-when a person uses their senses to gather info
-allows drivers to detect and identify a hazard in the roadway

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7
Q

Perception and Reaction Time
(average time)

A

-time it takes to detect, identify, and react to a hazard
-average is 1.6 seconds

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8
Q

Perception and Reaction Time
(Age of driver)

A

-Many elderly drivers won’t perceive and react to hazards as well as younger drivers
-declining cognitive functions

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9
Q

Perception and Reaction Time
(Location of the Hazard and time it takes to perceive it)

A

-directly in front quicker than peripheral
-saccade: process of moving a person’s eyes (can be as long as 1/3 of a second)
-avg perception/reaction time: 1.6 seconds
-hazard more than 15 degree from front can take as much as 1.7 sec. to move their head there and back

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10
Q

Perception and Reaction Time
(Nature of the Hazard)

A

while a driver may anticipate a red light, usually no warning that a child is about to run into the road
Infrequent encounters may lead to longer response times as the driver must determine how to handle unusual situations

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11
Q

Perception and Reaction Time
(Surrounding Circumstances)

A

-in more complex driving scenarios, perception and reaction time may increase
-if a driver’s in lose/lose scenario, may not react at all
-why civilian drivers may freeze as you approach

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12
Q

Perception and Reaction Time
(Distractions)

A

-longer perception and reaction time
-a human can’t multitask
-must quickly change is thought process from one task to another as rapidly as possible

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13
Q

Drive Defensively

A

-assume the worst and drive in a defensive manor
-driving too fast, rushing up to intersection, or tailgating won’t give civilian driver ample time to perceive and react
-may freeze up and fail to give right-of-way or make wrong decision and crash

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14
Q

Perception and Reaction Distance (depends on…)

A

-will depend on speed of the vehicle and the amount of time it takes to perceive and react
-if distracted, will increase substantially

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15
Q

Braking Distance (what it depends on and how it works)

A

-distance it takes a vehicle to brake to a stop
-directly related to how much kinetic energy the vehicle possesses at the time of the braking maneuver
-the energy depends on vehicle’s size and speed
-the more energy, the longer the distance to dissipate it and come to a stop
-brakes convert the kinetic energy into heat energy, dissipated into the atmosphere
-without enough time and distance to dissipate with the braking system, the kinetic energy is dissipated by skidding or crushing the vehicle

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16
Q

What is kenetic energy?

A

-energy in motion
-amount depends on vehicle’s size and speed

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17
Q

Function of brakes

A

the friction b/t the pad and drum creates heat, burns off the kinetic energy, slowing and stopping the vehicle

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18
Q

Skidding tires

A

-when not enough time and distance, driver is forced to slam on breaks, locking the wheels
-when brake pad is no longer rubbing against the disc/drum to create friction, converted to heat energy by the friction of tires rubbing across road

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19
Q

The more kinetic energy present when the vehicle strike the object, the greater the _____ is to the vehicle

A

Crush

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20
Q

Drag factor of the roadway will…

A

determine how well a vehicle is able to grab the roadway and come to a stop

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21
Q

Drag factor equation (𝒇)

A

(µ)(n)±m

where
µ = the coefficient of friction of the roadway
n = the braking efficiency of the vehicle
m = the slope of the road

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22
Q

Coefficient of Friction

A

-the “stickiness” of the road
-the higher the coefficient, the more sticky the road is
-typically range from 0.2-0.9

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23
Q

Braking efficiency

A

-how well the braking system will stop a skidding vehicle
-standard passenger vehicles assumed to be 100%, assuming the brakes are working and all 4 wheels lock
-fire apparatus won’t have 100% braking efficiency

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24
Q

Braking efficiency in fire apparatus

A

-truck tires: the stiff rubber doesn’t grip the road as well
-air brakes: takes time for air to travel through the brake system, enter complex brake chambers, and fully engage brakes (mechanical lag time or air pressure lag time)
-could be as low as 65%
-may add up to 100 ft of stopping distance

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25
Q

Braking distance: The skid to stop formula

A

SD = S² / (30)(𝒇)
Where
SD = stopping distance of vehicle in ft
S = speed of vehicle in MPH
𝒇 = drag factor, which is the coefficient of friction of the roadway adjusted for the road grade and braking efficiency of vehicle

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26
Q

Total Stopping Distance

A

brake distance + perception and reaction distance

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27
Q

Changing conditions that could affect Skid Distance

A
  • Speed: skid distance will increase as the vehicle’s speed increases, significantly longer(almost doubles) on a wet day
  • Slope of the Road: skidding downhill will be further than uphill
  • Braking Efficiency: could be as low as 65% on fire apparatus
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28
Q

Sight Distance

A
  • the distance of the roadway a driver can see ahead and to the sides
  • ensure enough sight distance to see oncoming traffic, then decide if they’re able to perform maneuvers such as
    1. stopping suddenly for hazard in roadway
    2. left turns against oncoming traffic
    3. looking L or R before accelerating onto highway
    4. passing another vehicle on a multi-line road
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29
Q

Key element to safe driving

A

ability to see oncoming traffic and then judge if there’s enough time and distance b/t oncoming vehicles to make a maneuver on a roadway

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30
Q

Stopping Sight Distance

A
  • the minimum sight distance required to perceive, react and safely stop should a driver encounter a hazard in the road
  • affected by rain, fog, smoke, hills, or curves
  • determine by calculating total stopping distance at the given speed
  • that distance in feet is the distance the driver must be able to see the hazard from (stoping sight distance)
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31
Q

Stopping Sight Distance and Speed Limits

A
  • where there is limited sight distance and the issue can’t be resolved through other means, traffic engineers may lower the speed limit
  • accomplishes 2 things:
    1. allows vehicle more time to make a maneuver
    2. reduce the stopping distance
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32
Q

Stopping Sight Distance and Emergency response

A

giving civilian drivers the time to recognize an emergency vehicle and make appropriate an diving decision is the key to providing them adequate notice of approach

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33
Q

G-Force

A

any change in direction of travel results in acceleration

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34
Q

Lateral Acceleration

A
  • when a vehicle changes direction
  • noticeable to the driver and passenger as centrifugal force
  • amount depends on speed and sharpness of turn
  • commonly referred to as “gs” or “g-force”
  • lateral g-force
35
Q

longitudinal g-force

A
  • front-to-back
  • from when vehicle accelerates or brakes
36
Q

How are handling characteristics judged?

A

amount of lateral g-force a vehicle can experience without rolling over or losing control

37
Q

How is cornering power calculated?

A
  • using the radius of a circle and the speed at which it broke traction
  • most fire apparatus will roll before breaking traction
38
Q

Rollover Threshold

A
  • relationship between the height of the center gravity and the track width
  • NFPA 1901 provides rollover threshold requirements
  • if unable to meet requirements, it must be equipped with ECS
39
Q

How do you calculate rollover threshold?

A
  • Track Width/2X hight of Center Gravity
  • or tilt table test
40
Q

What are the NFPA 1901 rollover threshold angle requirements?

A
  • Tilt table result no less than 26.5 degrees = 0.49
    -Height of CG no more than 80% of track width = 0.62
  • modern apparatus able to absorb just 0.50-0.60 lateral gs w/o rolling over
    -avg car can absorb 1.3-1.4 lateral gs
41
Q

Radius

A

how sharply the driver turns the steering wheel

42
Q

G-Force calculation

A

Speed² / Curve radius X 15

43
Q

Curve advisory speeds

A

limit the amount of lateral g-force experienced by the drive to no more than 0.15-0.20 gs

44
Q

90° intersection corner could be as low as 30-60ft. A speed as low as ___MPH may create enough g-force that exceeds the rollover threshold of the apparatus

A

15MPH

45
Q

steering-induced rollover

A

a driver who turns the wheel too sharply will create a curve in the road which may induce a rollover

46
Q

Weight Shift
(lateral)

A
  • lateral g-force begins to push on the side on the outside of the curve, causing it to sink into suspension
  • vehicle’s center of gravity will reduce track width, reducing rollover threshold
  • negative ffe
47
Q

Weight Shift
(longitudinal)

A
  • negative effect if vehicle brakes too hard, shifting weight to front axle, causing rear tired to be more likely to lock-up and skid
  • reducing the amount of weight shift from front to back is an important part of skid control. Done w/ smooth acceleration and braking
48
Q

Air Force P-18

A
  • added a special strut to reduce weight shift
  • raised rollover threshold to the point that it would break traction before rolling
49
Q

Slosh

A
  • will cause the water to push on inside of tank toward original direction of travel
  • especially dangerous w/ a partially loaded water tank, especially for wildfire tenders doing pump and roll ops
  • the inertia can cause the vehicle to lose steering control, incr stopping dist, or rollover
50
Q

Inertia

A
  • resistance of an object to any change in its speed or direction of motion
  • will cause the water to push on inside of tank toward original direction of travel
51
Q

Liquid Surge

A
  • where water is free to slosh back and forth
  • center of gravity shift causing sinking or shifting suspension
  • reduced rollover threshold
52
Q

Baffles
(and types)

A
  • partitions that help reduce energy of a surging liquid load
  • act as shock absorber
  • NFPA 1901 discuses two types:
    1. Containment method
    2. Dynamic Method
53
Q

Baffles
(Containment Method)

A

series of swash plates to divide the tank into a series of smaller, interconnected compartments

54
Q

Baffles
(Dynamic Method)

A
  • series of baffles to disrupt movement of water by changing its direction of travel
  • often staggered to create a turbulent motion that results in the water absorbing most of its own energy
55
Q

Case Study-Nevada

A

a partially filled tank contributed to factors of the rollover around a turn

56
Q

Three common scenarios of apparatus rollovers:

A
  1. rounds a curve too fast
  2. rounds a corner at an intersection too fast
  3. leaves road and rolls from overcorrecting. Usually due to entering curve too fast, distracted, or road collapses
57
Q

Tripped Rollovers

A
  • Caused when an object in vehicles path blocks movement of the wheels
  • can occur from curb, ditch, pothole, or a collapsing soft shoulder
  • factors include speed, height of object, and the suspension and tire deflection of the apparatus
58
Q

Untripped Rollovers

A
  • caused by frictional force b/t the tire and the road surface
  • AKA maneuver-induced rollover
  • more straight-forward to calculate speed
59
Q

Methods to increase rollover threshold

A
  1. incr track width and making vehicle wider
    • roads are only so wide
  2. lowering center of gravity and making vehicle lower
    • limited by type of vehicle
  3. stiffening suspension components
    • usually only option
60
Q

Benefits of stiffened suspension

A
  • incr vehicle’s resistance to lateral forces
  • reduced the amount of weight shift
  • gives better feedback to the driver as it’s driven closer and closer to the point of impended rollover
    • front tires start to lose traction and slide out, instead of starting to tip over
    • natural reaction will be to slow down providing warning and giving driver time to make corrections
    • in this scenario, be cautious on roads w/ high coefficient of friction (dry road), less warning before rollover
61
Q

Rollover Prevention

A
  • best way is to reduce speed
  • ensure weighed every year so its not overweight/overloaded
  • proper weight distribution
  • proper tank baffles
  • tires are maintained and properly inflated
  • thorough knowledge of zone and neighboring zones
  • don’t approach intersection too fast or slam on brakes
  • avoid drifting off road, if it does come to a complete stop, overcorrection can cause head-on collision or rollover
62
Q

US Air Force P-18 5 recommendations to increase rollover safety:

A
  1. audible or HUD to relay speed w/o taking attention away from driver
  2. speed governor
  3. Rollover Warning Device: warning of approaching roll angle or lateral force for rollover or slide out
  4. Black Box: tracking response of driver
  5. dual tires on Rear Axle
63
Q

Electronic Stability Control (ECS)

A
  • most vehicles are now equipped
  • Insurance Institute of Highway Safety (NIHS) defines as: a vehicle control system comprised of sensors and a microcomputer that continuously monitors driver’s steering input, selectively applies brakes and modulates engine power to keep vehicle traveling in path indicated by steering wheel position. Helps prevent sideways skidding and lose of control
  • “takes over” when vehicle begins to understeer, oversteer, or rollover
64
Q

Active Rollover Protection
(ARP)

A
  • will attempt to actively interrupt a vehicle about to roll over
  • will monitor the amount of force applied to lateral axis, apply brakes and reduce engine speed usually during Untripped Rollover caused by excessive speed or a sudden steering input
  • during Tripped Rollover, will engage an Active Suspension System, producing force in the opposite direction of the rolling force
65
Q

Rollover crash statistics

A
  • only 4.4% of tractor trailer accidents
  • but 58% of fatalities
  • 2% of all crashes in 2002
  • but nearly 1/3 of all fatal crashes
66
Q

Over-Braking

A
  • creates a longitudinal g-force grater than available friction of the road
  • more common on wet/slick roads
67
Q

Over-Braking
(unloaded fire apparatus)

A
  • brake system designed to handle fully loaded w/ full tank of water
  • more susceptible
  • prevent with smooth braking and accelerating
68
Q

Over-Accelerating

A
  • too much acceleration may turn the wheels hard enough to break traction
    -burnout
69
Q

Auxiliary Braking System

A
  • if used on wet/slick roads, an engine retarder or driveline retarder may cause vehicle to skid
  • if it creates more braking force on the wheels than the available friction b/t the tire contact patch and the road, the wheels may lock up and cause the tires to skid
70
Q

Friction can be used to:

A
  1. decelerate and stop the vehicle
  2. accelerate and drive the vehicle forward
  3. turn the vehicle in one direction or the other
  4. any combination of the above
71
Q

Friction circle

A
  • provide a visual representation of how grip is available to accelerate, brake, and turn
  • will differ based on several factor: speed, tire stiffness, air pressure, and axle weights
72
Q

The amount of friction available to use is equal to the _____ _____ (or stickiness) of the road way. Therefore the _____ of our friction circle will be equal to the drag factor of the road.

A
  • drag factor
  • radius
73
Q

Friction Circle Example Scenario

A
  • drag factor of dry, flat asphalt usually 0.75
  • radius of friction circle = 0.75
  • as long as the vehicle doesn’t generate more than 0.75 gs in lateral, longitudinal or combination, the tires will be able to hold their grip
  • truck tires usually grip about 80-85% of passenger cars
  • now we can examine how much g-force a vehicle can absorb before breaking traction
74
Q

Breaking and accelerating in curves

A
  • brake before the curve instead of in the curve
  • when at the edge of the friction circle (0.74 lateral gs of 0.75 limit), braking force gs combine w/ lateral gs, requiring more grip than the roadway has to offer
75
Q

Case Study - Maryland

A
  • more than likely, the causitive factor in the crash was the use of the engine retarder on a wet road
  • be sure to research type of aux brake the truck has and know if it should be disengaged in wet weather
76
Q

Understeer

A
  • front tire skid (UF)
  • lose steering control and will continue in straight line
  • pro racers refer to it as “push”
  • still dynamically stable, which is why manufactures strive to design the vehicle to understeer
  • natural tendency is to turn the wheel harder and slow down, which is the solution
77
Q

Oversteer

A
  • rear tire skid (OR)
  • will start to spin around, if it swings far enough, will spin out
  • known as “yaw”
  • main factors: weight dist., weight shift, suspension geometry, brake adjustments, tire stiffness, and tire pressure
  • considered to be more dangerous
  • to correct, steer in opposite direction of the turn (Counter-Steering), which is more complicated
78
Q

How do Antilock Brakes counter the loss of steering control caused by skidding tires?

A
  • prevent wheels from locking/skidding, allowing to still have lateral friction left for steering
79
Q

Left or Right Tire Skids

A
  • will pull to the side of the locking tires
  • known as tanking
80
Q

Full Tire Skids

A
  • will usually travel in a straight line
  • may drift to one side due to road crown for drainage
81
Q

Correcting understeer(UF) skid

A
  • ease off offending pedal
  • straighten wheel
82
Q

Correcting oversteer(OR) skid

A
  • turn into the skid (counter steer)
  • “look where you want to go”
    • the drivers brain and arms will work together to get the vehicle where it needs to be
83
Q

Wet/Dry Switch

A
  • in older apparatus
  • allows driver to reduce the pressure on the front brakes by up to half
  • severely reduces braking efficiency
  • should never be used (keep in dry mode)
84
Q

How to prevent skids

A
  • slow down
  • look down the road and anticipate hazards
  • smooth braking, accelerating, steering
  • aux brakes turned off in rain
  • caution w/ unloaded vehicles

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