Selection of Variables

Paul GreenUniversity of Michigan

Transportation Research Institute(UMTRI)

Simulator Users Group (SUG) meetingSession on Behavioral Simulator Fidelity

TRB Annual MeetingJanuary 13, 2004

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 ...?

Does the driver behave in the simulator the same way as on the road?

How large of a difference really matters?

The Ultimate Questions

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 Alzheimer’s disease not be advised to drive?

*ex3: How much hysteresis is acceptable in a steering system?

Who are we trying to convince?

Scientists and other technical experts ->

technical data presented in scholarly journals(or proceedings papers or reports)(publish or perish)

Nonscientists (public at large, legislators, etc)->

Videos / Outtakes no grainy face shots - reaction is apparent high quality audio - speech is easily understoodHands-on drives (if it is just a few people)(demo or die)

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)

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

Are signs and signals like the real thing?

Almost neverOversize compensationMUCTCD compliance (or other)

SignsMost current projection systems lack the res.Desired - arc minutes of resolution usually provide # of chan., FOV, format (XGA) computableSignals not enough luminance or contrast desired - luminance, contrast

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

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)

Is the in-vehicle task like the real thing?

OftenTouch screen vs. real deviceEase of instrumentation

No suggested measures of fidelity(task measures are time and errors)

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.

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

Is the environment like the real thing?

Probably more of an issue for military

and off-road driving (trees, buildings, etc.)

No measures suggested

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

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 speedStandard deviation of speedSpeed drops during taskLess commonThrottle varianceThrottle power spectrum (holds)

Lane departures (the definition problem aside)

What constitutes a lane departure? (12+ combos)

1. Which part of the vehicle matters?outer edge of side mirrorsoutside curve of bodyoutside edge of tire (contact or belly)tire centerline

2. Where on the line?touching the nearest edge linecenterline of the edgepast the farthest part of the edge line

Lane departuresStandard deviation of lane positionLess commonTLC (mean or some other %)%tile of lane position

headway distance or timeHeadway varianceLess common Coherence measuresTTC

Standard deviation of steering wheel angleLess commonSteering entropySteering power spectral distribution & related measures

How large of a difference really matters?

Practical vs. statistical significance

Other impairments - “It’s 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?)

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.

Summary: What Must We Report?(Green’s List)

If we ask for too much, people will not do it.

SubjectsAge

VehicleTLC uncontrolledWidth (for lane departure)Speed variability at fixed throttle angle (speed specific)Speed decay constantAcceleration at some partial throttle

RoadLane WidthShoulder width/distance to barrierAASHTO/MUTCD/etc. compliance

TrafficADTMixAggressiveness

LightingScene resolution (min of arc)Mean scene luminanceTraffic light/Brake light contrast ratio (& luminance)Mean center stack illumination (if relevant)

Any Questions?