vehicle motion human factors. chapter 2: #3, 6, 7
TRANSCRIPT
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Vehicle Motion
Human Factors
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• Chapter 2: #3, 6, 7
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Human Factors
• Rational Design of goods and services for people
• Primary human requirements– increased speed– increased range– increased capacity
• Secondary– safety, comfort & convenience, status
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Environment
• Where workspace is located– effects person’s performance
• lighting, noise, vibration, climate, pollutants
• Man - Machine - Environment interaction– want to optimize
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Human Variation
• Design is based on 90% of people
• Top and bottom 5% not in design– who’s not included?
• Adaptation & Instruction– want to limit instructions– How is a car laid out?– Where are the important components– Commonality
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Human Contact• Physical, Physiological, Biochemical
– Size– Reach– Strength– Body Composition
• Perception - Reaction– P-R, Info Processing, Motor Performance
• Cognitive and Social
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Pedestrians
• Important piece of urban design – Crosswalk placement– Social distance– Personal distance– Intimate distance
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Pedestrians
• How does personal space change ?– Transit– airplanes– waiting areas– cars
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How big is a pedestrian?
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Visual Acuity
• Contrast, brightness, illumination, relative motion
• Acuity decreases with increased visual angle
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Perception Reaction Time
• Time from stimulus to response
• Depends on complexity of info
• P-R 0.5 - 2.5 seconds depending on event type
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• Fig 2.2 pg 22 P-R times
• Expectancy– Continuity – experiences of the immediate past
are expected to continue– Event – Events that have not happened
previously will not happen– Temporal – for cyclic events the longer a given
state is observed the more likely it will change
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• Distance covered during P-R time– 1.47Vt
• Pedestrians– ~ 3.5fps, elderly pop ~3.0 fps just changed– Table 2.3
• DWI - Figure 2.3
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Lateral Displacement
• Driver moves away from objects on the side of the road
• Want to maintain a comfort zone between car and objects
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Lateral Displacement
• Closer objects is to pavement edge the more lateral displacement
• 3.3 ft for 8 ft lane
• 1.8 ft for 12 ft lane
• Can estimate lateral displacement – need l, v, d/dt
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Lateral Displacement
• Critical rate of change in visual angle– if d/dt is less than
critical assume collision
– l = a cot– dl/dt = -acsc^2d/dt
– d/dt = va/(a^2+l^2)
y
x a
l
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Lateral Displacement
• A vehicle traveling 40 mph was observed to displace laterally when it was 300 feet from a bridge abutment placed 6 feet to the right of the path. At what longitudinal distance from the same abutment would you expect the same driver to displace laterally when traveling 60 mph?
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Lateral Displacement
• What is critical rate of change (d/dt)– d/dt = {(40*1.47)*6}/(6^2 + 300^2) =
0.0039rad/sec– For 60mph– 0.0039 = {(60*1.47)*6}/(6^2 + L^2) – L = 368 feet
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Forces Acting on a Vehicle
• Propulsive (M)
• Resistance (R)
• Centrifugal (C)
• Weight (T)
• ma
• Supporting Forces (S)
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Resistance
• Inherent – vehicle is moving through something– R is a function of T and V
• Grade– adds resistance or increases speed
• Curvature– from centrifugal force – can be eliminated w/ banked curves
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Grade
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Curvature
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Vehicle Motion
• Superelevation e is the amount of banking in ft/ft on a curve
• e + f = v2/gr depends on speed– Table 2.4 – Values for f
• to negate f (no hands) e = v2/gr v in fps
• e= v2 /15R v in mph
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Vehicle Motion
• v=dx/dt
• a = dv/dt
• a=(dv/dx)v
• vdv = adx
• v =at + v0
• x = v0t +1/2(at2)
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Braking Distance• Db= (v2-v0
2)/2g(f+G)
• f = 11.2fps^2/32.2 = 0.348 used for design
• Not Brake type dependent – why?
• NOT Weight dependent - why?
• Does not account for reaction time
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Safe Stopping Distance
• Time to perceive and respond + time to brake to a stop
• P-R time =2.5s want to be conservative
• SSD = 1.47V(2.5) + (v2-v02)/2g(f+G)
•
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Decision Sight Distance
• Time to perceive and respond + time to brake to a stop
• P-R time =2.5s want to be conservative
• SSD = 1.47V(decision time) + (v2-v0
2)/2g(f+G)
•
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Example
• How long does it take a vehicle to brake to a stop from 60 mph– On a 5% downgrade– On a 5% up grade– On ice on a 5% upgrade
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Dilemma Zones
• Area around intersection - can’t stop can’t go –occurs when Yellow time is too short
• Need proper Y
• P-R time
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Dilemma Zones
• a2 is comfortable deceleration rate
– 4- 5 fps standing– 8 -10 fps seated
• xo > xc no problem
• xo <= xc dilemma
– Cannot cross intersection in Y+AR
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Dilemma Zones
• Can find minimum amber needed to eliminate dilemma zone
• Amber should be not more than 5 seconds
• Amber time = D/1.47V
• Assume 1s P-R time for signal
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Dilemma Zones• How long should the amber interval be for
the following:• Design Speed = 35mph• Intersection = 30 feet wide• Vehicle length = 15 feet• P-R time = 1 s
– Stopping distance = 1.47*35*1 + (35^2-0^2)/[30(0.0348)] = 169 feet
– Amber = 169/(1.47*35) = 3.28s
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Dilemma Zones• How long should the amber interval be for
the following:• Design Speed = 35mph• Intersection = 30 feet wide• Vehicle length = 15 feet• P-R time = 1 s
– Distance thru intersection= 168+30+15 = 213 ft– Amber = 213/(1.47*35) = 4.13s can use 3.28s Y
+ 1s AR