Module 5: Elements & Factors of Road Safety & Human Factors Flashcards
“Accidents.”
-There are no “accidents” in road safety.
-Accidents, and particularly street & highway accidents, do not happen, they are caused.
-The main reason “accident” is discouraged is because crashes or collisions can be prevented through design & technology.
Collisions/Crashes, Not Accidents.
The distinction is very fundamental:
-“Accidents” are things that inevitably happen & foster a dialog on
acceptable levels of such events.
-“Crashes” or “collisions” are events that can be avoided by design,
technology, & programmatic efforts. One can more easily aspire
to reduce collision events to zero, or towards zero.
Why are Injuries & Fatalities are Reducing in Canada?
-Road safety legislation.
-Improved vehicle technology.
Road Safety Legislation History in Ontario.
1971: Seatbelts required in all new vehicles
1976: Ontario first in North America to pass seatbelt law
1985: Tougher penalties for impaired driving
1990: Daytime running lights required in all new vehicles
1994: Graduated licensing program introduced
2007: Increased sanctions for street racing & aggressive driving. New sanctions for drivers with BAC between 0.05-0.0818.
2008: Increased sentences for impaired driving in Canada.
2009: New & young drivers must maintain a zero BAC. Hand-held cell phone use while driving banned. Electronic speed limiters required in large trucks to cap speed at 105 km/h.
Improved Vehicle Technology.
-Air bag
-Rear view camera
-ABS brake
-Seat belt
-Driver monitoring systems
-Forward collision systems
-Lane departure technology
-Blind spot detection
-Automatic emergency braking system
Contributing Factors in Fatal Collisions (2022).
-Distraction - 19.9%
-Speeding - 21.9%
-Impaired - 23%
-Fatigue - 2.8%
-Other human factor - 67%
-Environmental factor - 21.9%
-Vehicle factor - 3.5 %
-No contributing factors - 25.2%
Distracted Driving & Walking.
-20-30% of all vehicle fatalities (400 deaths annually).
-Primary distraction is the use of mobile phones.
-Other distractions include eating, adjusting GPS systems, & interacting with passengers.
-Studies estimate that 1 in 5 pedestrians involved in traffic crashes have been distracted, often by smartphones or listening to music.
-30-40% of pedestrians report using their phones while crossing streets.
How Distracted is Distracted Driving?
-Using a hands free electronic device is 4 times more distracting than talking to an adult passenger
-Texting while driving increases the risk of crashing by 23 times
-Dialling a phone increases the risk of crashing by 12 times
-Sending or reading a text message takes your eyes off the road for an average of 5 seconds. At 90 km/h, your vehicle will travel 125 m
No “Absolute” Safety.
-There is risk in all road transportation, regardless of the mode or combination of modes considered.
-That risk is inherent due to the variability of user behaviours, environmental conditions, & other factors over which no one has absolute control.
-Only “More Safe” or “Less Safe.”
Nominal Safety and Substantive Safety.
-Nominal safety is examined in reference to compliance with standards, warrants, guidelines, & sanctioned design procedures.
-Substantive safety is the actual long term or expected safety performance of a roadway. It is determined by observed collision frequency & severity over a period of time.
Safety Performance Measures.
-Collision frequency.
-Collision rate.
Collision Frequency.
-For a section of road = number of collisions per km per year
-For an intersection = number of collisions per year
-Collision frequency is a function of traffic volumes.
Collision Rate.
-More meaningful as a safety performance measure.
-For a section of road = number of collisions per million vehicle km
-For an intersection = number of collisions per million vehicle
-It measures the risk faced by the road users
-Collision rate varies with traffic volume
Safety Performance Function.
-Safety Performance Function is the kind of function that describes the safety of a certain road when serving different traffic levels
-It estimates the expected average crash frequency for a given
average traffic volume.
Collision Modification Factor.
-Collision Modification Factor is a multiplicative factor that indicates the proportion of crashes that would be expected after implementing a countermeasure.
-It measures the effectiveness of safety improvements.
Human Factors.
Human Factors help us understand:
-How drivers use the roadway environment
-Driver reactions in unusual situations
Understanding Human Factors.
-By developing an understanding of the role human factors in collisions, designers may be able to better adapt their designs to driver, pedestrian, & cyclist needs, & thus reduce the road safety risks faced by all road users.
Two Foundational Principles.
-If perceptual clues are clear & consistent, the task of adaptation is made easier & the response of drivers will be more appropriate & uniform.
-For roadway design this translates into two foundational principles:
-Driver Expectancy - Design a roadway so that it conforms to what
drivers expect from such a roadway based on previous
experience.
-Driver Perception & Reaction - Provide drivers with sufficient time to detect, identify, & react to hazards in the roadway.
Driver Expectancy.
-Prior driver experiences develop, over time, into a set of expectancies, which:
-Allow for anticipation & forward planning
-Enable drivers to respond to common situations in predictable &
successful ways.
-If these expectancies are violated, it may lead to a wrong decision or result in longer reaction time.
Effects of Driver Expectancy.
-Drivers anticipate common situations
-Predictability reduces errors
-Unexpected creates difficulties
-Drivers assume standard situations
-Upstream creates expectancies
-Upstream also conditions drivers
-Transition engender problems
-Expectancies are associated with all operations
Perception Reaction Time.
PRT = The period between the occurrence or appearance of a signal (visual stimulus) & the initiation of the driver’s physical reaction to it.
-A complex, unexpected decision with several alternatives yields a considerably longer reaction time than a simple, anticipated decision.
-Long processing times also decrease the time available to attend to other information & thus compound the chances for error.
Four Elements of PRT.
-Detection: sees a visual target
-Identification: identifies the signal & understands the stimulus
-Decision: decides what action to take
-Response: initiates the action decided upon
Unalerted Drivers.
-Selective Attention: When we drive, our brains filter visual stimuli to focus our attention on things we need to notice to operate our vehicle safely.
-Inattentional Blindness: When we drive we sometimes miss critical information even when our eyes are focused on the road ahead.
High Workload Causes Inattentional Blindness.
-A higher mental workloads may cause inattentional blindness.
-Research shows that focus upon a particular object may result in inattentional blindness.
-This may result in a failure to notice objects on the road such as stop signs, speed limit indicators or even other cars.
-You drive while carrying a conversation on the cell phone. You fail
to pay attention to a cab swerving into your lane, & end up having
a collision.
-Therefore, design roads that require less driver’s workload.
Driver Workload.
-Workload: effort & attention to do a task
-Drivers keep workload within a range:
-High workloads may lead to speed reductions
-Unfamiliar drivers will have higher workloads
-Speed variance can increase
-Higher workloads
-Complex road geometrics
-Urban areas
Factors Influencing Driver Workload.
-Time available to respond to a situation
-Sight distance
-Operating speed
-Distance between intersections/driveways
-Presence of other features
-Recently encountered road features
The Designer’s Response.
-Recognize expectations
-“Design in” predictability
-Provide internally consistent designs
-Provide positive guidance
-Provide adequate sight lines/distance
-Consider cumulative effects of different design decisions
-Reduce the cognitive workload
Basic Principles.
-Drivers anticipate common situations
-Predictability reduces errors
-Expectancies reduce perception reaction times
-Unexpected creates difficulties
-Drivers assume standard situations
-Upstream creates expectancies
-Transitions lead to problem
-High workload increases collision potential
Importance of Design.
It is important to have:
-Conformity to driver’s expectations
-Design consistency
-Clear & direct guidance & simple choice for drivers reduce driver
workload.
-Clear sight lines & adequate sight distances to allow time or
decision making.
Superiority Bias.
-When it comes to driving, most people think their skills are above average.
-Drivers think they can drive better & safer & faster than others.
Driving Too Fast Unintentionally.
Situations that can lead to an underestimation of driving speed:
1. If a motorist has been driving at a high speed for a long time.
2.In transitional situations: exiting a freeway, long stretch of straight road into a series of bends, etc.
3. When there is little peripheral information: nighttime, fog, etc.
4. When the driver’s position is considerably above the road surface.
Drivers Tend to Drive Faster.
-Wider lane
-More number of lanes
-Wider roadside free zone
-Presence of lane marking
-Straighter road
-Smoother road surface
-Less buildings or vegetation
-Less outside noise
Driver Adaptive Behaviours.
-Drivers respond to geometric demand:
-Risk perception
-Limited sight distance, sharp curve
-Visual search pattern change:
-Open highway - less focus
-Urban car following - more concentrated
-First time users vs regular commuter
The Influence of Design.
-Where do drivers lower speed?
-sharp curves
-limited sight distance
-crest vertical curves
-narrow roads, deep ditches
-Not at intersections where risk is higher
-Speed signs have little influence
Speed Adaptation.
-Some Practical Context:
-drivers adapt to driving at higher speeds
-extended periods lead to difficulties in slowing down
-physical clues are the best inducements
-speed adaptation effects could last up to 5-6 min
Highway 104 Toll Plaza - Collision Analysis.
-Severity weighted collision rate:
-73% higher than the rest of Highway 104
-117% higher than all 100 series highways
-Fatal collision over-represented
-Toll plaza approached (+/- 2km) - 34 collisions in 5 years
Collision Vectors.
-Speed
-Roadside design
-Plaza conspicuity
What is Vision Zero?
-Vision Zero is a public program that aims to have zero fatalities or serious injuries from road traffic crashes.
-It redefines road safety by taking a public health approach to collisions.
-Responsibility for collisions is shared between road users, system designers, & policy makers.
-It also provides a toolkit of design & enforcement methods.
Vision Zero Approach.
Traditional Approach:
-Traffic deaths are inevitable
-Perfect human behaviour
-Prevent collisions
-Individual responsibility
-Saving lives is expensive
Vision Zero Approach:
-Traffic deaths are preventable
-Integrate human failing in approach
-Prevent fatal & severe crashes
-Systems approach
-Saving lives is not expensive
The 5 E’s of Traffic Safety.
-Engineering
-Education
-Enforcement
-Evaluation
-Engagement
Vision Zero - Design Elements.
-Smaller block sizes, frequent street connections, narrower streets
-Traffic calming
-No right turn on red
-Clear crossings; medians & refuge islands
-Pedestrian only areas & basic, consistent sidewalks
-Protected bicycle lanes & special attention at intersections
-Safety improvements around mass transportation & corridors
Median Barrier.
-Cross-median collisions are one of the most severe types of collisions.
-Median barriers decrease collision severity but increase collision frequency/
Roundabout.
-Intersections are high collision areas.
-Roundabouts tend to slow down vehicle speeds.
-It reduces frequencies of certain collision types and reduces severity of collisions.
Speed Hump.
-Reduces vehicle speeds by forcing drivers to slow down.
Pedestrian Island.
-A safe place to wait.
-Helpful for elderly & wheelchair users.
Enforcement.
-Speed cameras
-Red light cameras
-Seat-belt ignition interlocks
-Alcohol interlocks
