Vehicle Motion

Human Factors

• Chapter 2: #3, 6, 7

Human Factors

• Rational Design of goods and services for people

• Primary human requirements– increased speed– increased range– increased capacity

• Secondary– safety, comfort & convenience, status

Environment

• Where workspace is located– effects person’s performance

• lighting, noise, vibration, climate, pollutants

• Man - Machine - Environment interaction– want to optimize

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

Human Contact• Physical, Physiological, Biochemical

– Size– Reach– Strength– Body Composition

• Perception - Reaction– P-R, Info Processing, Motor Performance

• Cognitive and Social

Pedestrians

• Important piece of urban design – Crosswalk placement– Social distance– Personal distance– Intimate distance

Pedestrians

• How does personal space change ?– Transit– airplanes– waiting areas– cars

How big is a pedestrian?

Visual Acuity

• Contrast, brightness, illumination, relative motion

• Acuity decreases with increased visual angle

Perception Reaction Time

• Time from stimulus to response

• Depends on complexity of info

• P-R 0.5 - 2.5 seconds depending on event type

• 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

• 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

Lateral Displacement

• Driver moves away from objects on the side of the road

• Want to maintain a comfort zone between car and objects

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

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

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?

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

Forces Acting on a Vehicle

• Propulsive (M)

• Resistance (R)

• Centrifugal (C)

• Weight (T)

• ma

• Supporting Forces (S)

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

Grade

Curvature

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

Vehicle Motion

• v=dx/dt

• a = dv/dt

• a=(dv/dx)v

• vdv = adx

• v =at + v0

• x = v0t +1/2(at2)

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

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)

•

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)

•

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

Dilemma Zones

• Area around intersection - can’t stop can’t go –occurs when Yellow time is too short

• Need proper Y

• P-R time

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

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

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

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