6 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
7 Design Driver Wide range of system users What 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
8 Picture this: A little old lady who is used to her 5,000-lb 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.
10 Visual Acuity
11 Visual Reception Visual 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
12 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
13 Visual Reception Color 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
14 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
15 Visual Reception Depth perception –Ability to estimate speed and distance Passing on two-lane roads Signs are standardized to aid in perceiving distance
16 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?
17 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 times need 2x brightness for each decade past 25
20 Perception-Reaction Process Perception Identification Emotion Reaction (volition) PIEV Used for Signal Design and Braking Distance
21 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
22 Typical Perception-Reaction time range is: 0.5 to 7 seconds Affected by a number of factors. What are they?
23 Perception-Reaction Time Factors Environment: Urban vs. Rural Night vs. Day Wet vs. Dry Age Physical Condition: Fatigue Drugs/Alcohol Distractions
24 Perception-Reaction Time Factors medical condition visual acuity ability to see ( lighting conditions, presence of fog, snow, etc ) complexity of situation ( more complex = more time ) complexity of necessary response expected versus unexpected situation ( traffic light turning red vs. dog darting into road )
26 Perception Reaction Time (PRT) Time from Perception to Initial Reaction to Stimulus (Example)
27 Age Older drivers –May perceive something as a hazard but not act quickly enough –More difficulty seeing, hearing, reacting –Drive slower
28 Age Younger 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 Reaction by Joseph E. Badger.
29 Alcohol Affects each person differently Slows reaction time Increases risk taking Dulls judgment Slows decision-making Presents peripheral vision difficulties Human Factors - Perception and Reaction by Joseph E. Badger.
30 From: Driver Characteristics and Impairment at Various BACs H. Moskowitz, M. Burns, D. Fiorentino, A. Smiley, P. Zador
31 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?)
32 Weather Fog Rain Ice Snow affects ability to see (snow, fog) changes ability to stop (ice, snow, wet)
33 Understanding Flashing DON’T WALK
34 Understanding Count down signal
37 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” mean Many people, especially older drivers, don’t understand meaning of left turn displays Human Factors - Perception and Reaction by Joseph E. Badger.
38 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 Reaction by Joseph E. Badger.
39 D p = 1.47(V)(t) where: D p = Distance traveled during PIEV process (feet) V = velocity (mph) t = perception-reaction time = 2.5s
40 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 seconds D p = 1.47(V)(t) = 1.47(65 mph)(2.5 sec.) ~ 240 feet Impaired Driver has P/R time of 4 seconds D p = 1.47(65 mph)(4 sec) ~ 380 feet Difference is 380 – 240 = 140 feet Difference is safety and economic problem! Example
41 Perception/Reaction Applications Stopping sight distance Passing sight distance Placement of signs/traffic control devices Design of horizontal/vertical curves
42 Driver Expectancy
43 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:
45 Driver Expectancy Driver 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.
46 Driver Expectancy Reduce load on driver Simplify driving task Try 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???
47 Selection of Design Driver
48 Design criteria must be based on the capabilities and limitations of most drivers and pedestrians
49 The 85 th percentile is generally used to select Design Criteria The 95 th percentile or higher is used where the consequences of failure are severe AASHTO recommends 2.6 seconds for stopping sight distance (90 th )
50 Role of Transportation Engineer allow proper sight distance in design, sign placement avoid hitting driver with too much info at once –one sign at a time clarity (sign size, color, reflectivity)
51 Driver Activities in Selection of Path Control (overt actions) –Road Edge –Avoid a Car Guidance (decisions) –Lane Placement –Car Following –Passing
52 Driver Activities in Selection of Path Cont. Navigation Level (planning) –Maps –Observe a directional sign
53 Pedestrians Characteristics similar to driver Design of pedestrian facilities Signal timing – get peds across during red phase
54 Pedestrians Walking Speed varies between 3 to 8 ft/sec Design value is 4 ft/sec Used to calculate safe pedestrians crossing time
55 Bicycles On-road Separate facilities Similar 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