Selection of Variables

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Selection of Variables Paul Green University of
Michigan Transportation Research
Institute (UMTRI) Simulator Users Group (SUG)
meeting Session on Behavioral Simulator
Fidelity TRB Annual Meeting January 13, 2004
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What do we want to know? What is the question we
need to answer? Who are we trying to
convince? Is the road like the real thing? Is
the traffic ...? Are signs and signals ...? Is
visibility like ...? Does the vehicle handle
...? Is the in-vehicle task ...? Are the
drivers? Is the environment ...? Does it sound
...?
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The Ultimate Questions
Does the driver behave in the simulator the
same way as on the road? How large of a
difference really matters?
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What is the question we need to answer? What we
measure is an answer, so we need to know what is
the question. ex1 Does dialing a cell phone
while driving significantly increase the
probability of a crash at signalized
intersections? ex2 Under what kinds of
situations should a person with a particular
stage of Alzheimers disease not be advised to
drive? ex3 How much hysteresis is acceptable
in a steering system?
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Who are we trying to convince?
Scientists and other technical experts -gt
technical data presented in scholarly
journals (or proceedings papers or
reports) (publish or perish) Nonscientists
(public at large, legislators, etc)-gt Videos /
Outtakes no grainy face shots - reaction is
apparent high quality audio - speech is easily
understood Hands-on drives (if it is just a few
people) (demo or die)
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Is the road like the real thing?
AASHTO compliance? We often study open road
driving. We often measure is influenced
by ( should be reported) Lateral
control lane width curve
radius Longitudinal control posted speed,
natural speed of the road (shoulders,
set backs)
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Is the traffic like the real thing?
Amount (ADT or), not light or heavy Traffic mix
(cars, trucks, SUV/minivans, motorcycles,
pedestrians) will matter for following
studies focus is on cars (but non-cars
outnumber cars) following large vehicle
results in steadier driving but reduced
ability to see ahead rarely
reported Vehicle/pedestrian aggressiveness
we do not know how to measure this never
reported
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Are signs and signals like the real thing?
Almost never Oversize compensation MUCTCD
compliance (or other) Signs Most current
projection systems lack the res. Desired - arc
minutes of resolution usually provide of
chan., FOV, format (XGA) computable Signals
not enough luminance or contrast desired -
luminance, contrast
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Is visibility like the real thing?
Primary issues daylight - too dim by orders of
magnitude night driving - no enough contrast
for lighting desired data - mean scene
luminance, mean center stack illumination,
brake light contrast ratio signs signals
mentioned earlier Secondary issues sight
distance in fog
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Does the vehicle handle like the real thing?
Note I have ignored motion, an important topic,
because I do not know enough about it to proved
informed suggestions. Case 1 Normal driving
(common) unspecified TLC - railroad tracks
problem (measure) road imperfections, cross
winds, tire pressure excess speed stability
perfectly flat, no head/tail wind desire
speed decay (rolling resistance) desire
throttle response (acceleration) Case 2 Evasive
maneuvers (less common) need input from vehicle
dynamics folks on this (lots of HFEs are
psychologists)
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Is the in-vehicle task like the real thing?
Often Touch screen vs. real device Ease of
instrumentation No suggested measures of
fidelity (task measures are time and errors)
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Are the drivers (subjects) like of real drivers?
I test students because They are easier to
get They cost less They understand the
instructions There are fewer IRB concerns
Their performance is less variable If your
question concerns drivers of all ages, especially
if it relates to the use of technology, include
older subjects (e.g., over 65) in the sample.
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Does it sound like the real thing?
Prior UMTRI work showed sound has little effect
on basic driving performance. Modern motor
vehicles are quiet. Only usually matters
(masking) auditory warning speech I/O No
measures suggested
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Is the environment like the real thing?
Probably more of an issue for military and
off-road driving (trees, buildings, etc.) No
measures suggested
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Does the driver behave in the simulator the
same way as on the road?
Sometimes yes, sometimes no No consequence of
leaving lane No consequence of poor speed
control No consequence of poor situation awareness
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Suggested Driving Performance Measures
It really depends on the question But here is
what is sometimes reported. (Comment on each -
ease of measurement, crash/behavioral
implications) Mean speed Standard deviation of
speed Speed drops during task Less
common Throttle variance Throttle power spectrum
(holds)
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Lane departures (the definition problem aside)
What constitutes a lane departure? (12
combos) 1. Which part of the vehicle
matters? outer edge of side mirrors outside
curve of body outside edge of tire (contact or
belly) tire centerline 2. Where on the
line? touching the nearest edge line centerline
of the edge past the farthest part of the edge
line
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Lane departures Standard deviation of lane
position Less common TLC (mean or some other
) tile of lane position headway distance or
time Headway variance Less common Coherence
measures TTC Standard deviation of steering
wheel angle Less common Steering entropy Steering
power spectral distribution related measures
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How large of a difference really matters?
Practical vs. statistical significance Other
impairments - Its like being drunk. Do not
forget to report means Do not forget about
significant figures (What does a standard
deviation of lane position of .213 m mean?)
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The problem is that we do really know which
measures are best, in part, because we do not
have a theory that describes how people drive.
We need a science of driving.
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Summary What Must We Report? (Greens List)
If we ask for too much, people will not do
it. Subjects Age Vehicle TLC uncontrolled Width
(for lane departure) Speed variability at fixed
throttle angle (speed specific) Speed decay
constant Acceleration at some partial throttle
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Road Lane Width Shoulder width/distance to
barrier AASHTO/MUTCD/etc. compliance Traffic ADT
Mix Aggressiveness Lighting Scene resolution
(min of arc) Mean scene luminance Traffic
light/Brake light contrast ratio (
luminance) Mean center stack illumination (if
relevant)
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Any Questions?