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Design Driver

CE 453 Lecture 7

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Design Driver Characteristics

Design Driver: driver most expected to use facility (familiar or unfamiliar?) – Accommodated in design, signing, etc.

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Design Driver Characteristics Cont.

Physical characteristics Processing ability Tolerable Accelerations/Decelerations – Longitudinal (along roadway )– Lateral (around curves) – Vertical (comfort)

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Design Driver Characteristics Cont.

Others?: age, gender, physical condition (alcohol, etc.), mental capabilities, skill (self perception – are you in the top ½ of driver skill?) Two others related to design: perception-reaction time and expectancy

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Design Driver

Wide range of system usersWhat range of drivers use the system?– Ages: 16 year old to 80 year old– Different mental and physical states– Physical (sight, hearing, etc)– experience

Design Driver: driver most expected to use facility

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Picture this: A little old lady who is used to her 5,000-lb. 1971 Buick LeSabre Centurion Estate Station Wagon is tonight poking along in her grandson's brand new Suzuki Samurai - in the rain - on an unfamiliar road after spending four hours drinking fuzzy navels at her 50th class reunion at Neil Cosgrove's Friendly Bar & Grill.

Compare her to the 13-year-old who swiped Dad's keys and is now piloting Dad’s Porsche at Mach II down the same stretch of unfamiliar road. These two unlikely individuals inadvertently attempt to occupy the same space simultaneously. Yet you certainly can't apply the same perception and reaction times to both drivers.

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80-8

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> 8

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Age Groups

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Visual Acuity

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Visual ReceptionVisual Acuity: Ability to see fine details

• Static (stationary objects): – Depends on brightness– Increases with increasing brightness up to ~ 3 candles (cd/sq ft) -- remains

constant after that– Contrast– Time (0.5 to 1.0 second)

• Dynamic (ability to detect moving objects)– Clear vision within a conical angle 3 to 5º– Fairly clear within 10 to 12º– Key criteria in determining placement of traffic signs

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Visual Reception

Peripheral Vision: Ability to see objects beyond the cone of clearest vision (160 degrees) – Age dependent– Objects seen but details and color are not clear

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Visual ReceptionColor Vision: Ability to differentiate one color from another– Lack of ability = color blindness– Combinations to which the eye is the most sensitive

• Black and white• Black and yellow

Key in determining traffic signs colors

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Visual Reception

Glare Recovery: Ability to recover from the effects of glare

• Dark to light : 3 seconds -- headlights in the eye• Light to dark: 6 seconds – turning lights off• Usually a concern for night driving

Need to provide light transitions

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Visual ReceptionDepth perception– Ability to estimate speed and distance

• Passing on two-lane roads• Signs are standardized to aid in perceiving

distance

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From GB:Some 75-year old drivers require how many times the more brightness at night to receive visual information than a 25-year old driver?

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Some 75-year old drivers require how many times more brightness at night (to receive the same visual information) than a 25-year old

driver?

32 timesneed 2x brightness for each decade past 25

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Hearing

Hearing perception– Ability to detect warning sounds– Sirens, horns

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Perception/Reaction Time

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Perception-Reaction Process

PerceptionIdentification

EmotionReaction (volition)

PIEVUsed for Signal Design and Braking Distance

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Perception-Reaction Process

Perception– Sees or hears situation (sees deer)

Identification– Identify situation (realizes deer is in road)

Emotion– Decides on course of action (swerve, stop, change lanes, etc)

Reaction (volition)– Acts (time to start events in motion but not actually do action)

• Foot begins to hit brake, not actual deceleration

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Typical Perception-Reactiontime range is:

0.5 to 7 seconds

Affected by a number of factors.What are they?

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Perception-Reaction Time FactorsEnvironment:

• Urban vs. Rural• Night vs. Day• Wet vs. Dry

AgePhysical Condition:

• Fatigue• Drugs/Alcohol

Distractions

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Perception-Reaction Time Factors

medical conditionvisual acuityability to see (lighting conditions, presence of fog, snow, etc)complexity of situation (more complex = more time)complexity of necessary responseexpected versus unexpected situation (traffic light turning red vs. dog darting into road)

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Perception Reaction Time (PRT)

Time from Perception to Initial Reaction to Stimulus (Example)

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Age

Older drivers – May perceive

something as a hazard but not act quickly enough

– More difficulty seeing, hearing, reacting

– Drive slower

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AgeYounger drivers– May be able to act quickly but not have experience to recognize

things as a hazard or be able to decide what to do– Drive faster– Are unfamiliar with driving experience– Are less apt to drive safely after a few drinks– Are easily distracted by conversation and others inside the

vehicle– May be more likely to operate faulty equipment– Poorly developed risk perception– Feel invincible, the "Superman Syndrome”

Human Factors - Perception and Reactionby Joseph E. Badger. jebadger@harristechnical.com

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Alcohol

Affects each person differently Slows reaction time Increases risk taking Dulls judgment Slows decision-making Presents peripheral vision difficulties

Human Factors - Perception and Reactionby Joseph E. Badger. jebadger@harristechnical.com

30From: Driver Characteristics and Impairment at Various BACsH. Moskowitz, M. Burns, D. Fiorentino, A. Smiley, P. Zador

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Experience

Even NASCAR drivers practice

Familiarity Faster on familiar Unfamiliar more distracted– Rental car on unfamiliar road at 10 pm when it starts to rain (What is the driver doing?)

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Weather

Fog Rain Ice Snow affects ability to see (snow, fog) changes ability to stop (ice, snow, wet)

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Understanding

Flashing DON’T WALK

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Understanding

Count down signal

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Understanding

Most people do not reduce speed in a work zone until they actually see activity Only 78% of drivers in a study understood what “Lane Ends” meanMany people, especially older drivers, don’t understand meaning of left turn displays

Human Factors - Perception and Reactionby Joseph E. Badger. jebadger@harristechnical.com

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Fatigue

Increases perception/reaction time Study by American Automobile Association found that in 221 truck accidents only 18.4% of the drivers had been driving less than nine hours. 41% of truck accidents

Human Factors - Perception and Reactionby Joseph E. Badger. jebadger@harristechnical.com

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Dp = 1.47(V)(t)

where:Dp = Distance traveled during PIEV process (feet)V = velocity (mph)t = perception-reaction time = 2.5s

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How much longer does it take an impaired driver to perceive/react than an unimpaired one at 65 mph?

Unimpaired has P/R time of 2.5 secondsDp = 1.47(V)(t) =

1.47(65 mph)(2.5 sec.) ~ 240 feetImpaired Driver has P/R time of 4 seconds

Dp = 1.47(65 mph)(4 sec) ~ 380 feet

Difference is 380 – 240 = 140 feetDifference is safety and economic problem!

Example

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Perception/Reaction Applications

Stopping sight distancePassing sight distancePlacement of signs/traffic control devicesDesign of horizontal/vertical curves

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Driver Expectancy

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Driver Expectancy

Expectancy (def) – an inclination based on previous experience to respond in a set manner to a roadway, traffic, or information situation Types – A Priori – long-term (based on collective past

experience) PRT = 0.6s avg., some 2.0s– Ad Hoc – short-term (based on site-specific

practices/situations encountered during a particular trip on a particular roadway, PRT = 1.0s avg., some 2.7s

Reaction time and car accident applet: http://www.phy.ntnu.edu.tw/java/carDistance/carAccident.html

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http://www.sdt.com.au/STOPPINGDISTANCE.htm

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Driver ExpectancyDriver Expectancies (what do we expect as drivers?)– Specific colors (red = stop)– Driver ahead not to decelerate rapidly– Slower drivers in right lane– Work zone signs = people working– Lane size– Etc.

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Driver Expectancy

Reduce load on driverSimplify driving taskTry to keep roadway environment within “expected parameter”– Traffic control

• Consistent size, color, shape– Design features – depends on functional class

• Fwys expect 12 foot lanes

Can this foster complacency???

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Selection of Design Driver

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Design criteria must be based on the capabilities and limitations of most drivers and pedestrians

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The 85th percentile is generally used to select Design Criteria

The 95th percentile or higher is used where the consequences of failure

are severe

AASHTO recommends 2.6 seconds for stopping sight distance (90th)

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Role of Transportation Engineer

allow proper sight distance in design, sign placementavoid hitting driver with too much info at once– one sign at a time

clarity (sign size, color, reflectivity)

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Driver Activities in Selection of Path

Control (overt actions) – Road Edge– Avoid a Car

Guidance (decisions) – Lane Placement– Car Following– Passing

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Driver Activities in Selection of Path Cont.

Navigation Level (planning) – Maps– Observe a directional sign

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Pedestrians

Characteristics similar to driverDesign of pedestrian facilitiesSignal timing – get peds across during red phase

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Pedestrians

Walking Speed varies between 3 to 8 ft/sec

Design value is 4 ft/sec

Used to calculate safe pedestrians crossing time

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BicyclesOn-roadSeparate facilitiesSimilar to driver (perception-reaction)Divided by AASHTO into 3 classes– Class A: experienced or advanced bicyclists

• Consider bike as a vehicle and ride comfortably with traffic• Usually not allowed on freeways

– Class B: less experienced bicyclists• Usually prefer neighborhood streets and bike facilities

– Class C: children on their own or with parents• Mainly residential