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Steering Behaviors for Autonomous Vehicles in Virtual Evironments
Hongling Wang
Joseph K. Kearney
James Cremer
Department Of Computer Science
University of Iowa
Peter Willemsen
School of Computing
University of Utah
Focus• Control of Autonomous Vehicles in VE
– Ambient traffic– Principal roles in scenarios
• Importance of Road Representation– Frame of reference– Natural coordinate system
• Intersection and Lane Changing Behaviors– Complex interactions among vehicles
• Limits of independent control
Motivation• VE as Laboratories for Studying Human Behavior
– Developmental differences in road crossing– The influence of disease, drugs, and disabilities– Design of in-vehicle technology
• Cell phones, navigation aids, collision warning
Bicycle Simulator Video
Gap Acceptance in the Hank Bicycle Simulator
Related Work
• Flocking– Complex group behavior from simple rule-based behaviors
(Reynolds)
• Hierarchical Distributed Contol– Independent, goal-oriented sub-behaviors (Badler et al.; Blumberg
and Galyean; Cremer, Kearney, and Papelis)
• Driving– Simulation (Donikian; Lemessi)
– ALV (Coulter, Sukthankar; Wit, Crane, and Armstrong)
– Human Driving Behavior (Ahmed; Boer, Kuge, and Yamamura; Fang, Pham, and Kobayashi; Salvucci and Liu)
Roadway Modeling• Roads as Ribbons
– Oriented Surface
– Smooth Strips
– Twist and turn in space
• Central Axis– Arc-length parameterized curve
• Twist Angle• Linked through Intersections
Ribbon• Ribbon coordinate system
– Distance, Offset, and loft (D,O,L)
• Egocentric frame of reference• Efficient Mapping (D,O,L) (X,Y,Z)
Intersections—Where Roads Join
• Shared regions• Non-oriented• Corridors connect incoming and outgoing lanes
– Single lane ribbons– Annotated with right-of-way rules
Ribbon to Ribbon Transitions• Problem: Tangle of Ribbons
Bookkeeping Tedious and Error Prone• Possible switch in orientation• Possible shift in alignment
• Solution: Paths • Composite ribbons
Path
• One-lane Overlay– Removes transitions
between ribbons
• Immediate Plan of Action- Highly dynamic- Natural frame of reference
Distributed Control
• Multiple, Independent Controllers– Each responsible for some aspect of behavior
• e.g. Cruising, Following
– Compete for control
• Control Parameters– Acceleration– Steering Angle
Road Tracking
• Non-holonomic constraint
Rolling wheels
Move on a circle
• Pursuit point control– Steer to a point on the path– Look-ahead distance
Controlling Speed
• Cruising: Proportion Control
• Following: Proportional Derivative Controller
)()( vKsKfa f
vfp
)( vvKca d
cp
Intersection Behavior Gates access to shared regions
– Decision:
Go / No Go– Action:
stop at stopline
Gap Acceptance Based on Interval Analysis
– Right-of-way rules encoded in DB– Corridors as resources
Compare crossing intervals
time
c0
tenter texit
c2c1
Intersection Exceptions Problem: deadlock
Double blocked threats• Solution:
Recognition and response
Problem: starvationUnending stream of opposition
• Solution: Guaranteed progress
)2/(2 sva
What’s missing?
• Where do paths come from?– Vehicles meander
Pick corridors
Add outgoing road
• No goal seeking behavior– Need directions
“Turn right at the first intersection,
drive through two intersections,
and then turn left.”
Route
• A succession of roads and intersections– Like MapQuest Directions
• A global, strategic goal – The path must conform to the route
• May require lane changes
Stages of Lane Changing
• Motivation
Why change lanes?
• Decision Choosing a target lane
Deciding when to go
• Action How to change lanes?
Motivation to Change Lanes– Discretionary Lane Change (DLC) to improve driving conditions (e.g. speed, density)
– Mandatory Lane Change (MLC) to meet destination requirements (e.g. lane termination)
Decision to Initiate a Lane Change– Best conditions (e.g. flow)– Gap Acceptance
• Lead gap• Lag gap
Lane Changing Action
• Shift Pursuit Point– Proportional Derivative
Controller
– Speed Coupling
)()( oKotoKo LC
vLCp
Behavior Combination
• Combine accelerations from– Cruising behavior– Following behavior– Intersection behavior
• Combine steering angle from– Tracking behavior– Lane changing behavior
Interactions Between Controllers
Problem: impeded progressFollowing prevents overtaking
• Solution: Reduce following distance
Stiffen controller
Problem: unveiled threatAppearance of leader in new lane
• Solution: Split attention – follow 2 leaders
Summary
• An accurate, efficient, robust roadway model– Ribbon network– Arc length parameterization– Efficient mapping between ribbon and Cartesian
coordinates
• A framework for modeling behaviors– Ribbon based tracking– Path based behaviors– Route as a strategic goal
Future Work
• Pedestrians
• Modeling non-oriented navigable surfaces
(e.g. intersections)
• Pursuit Point Control
• Behavioral Diversity
Acknowledgments
• NSF Support: INT-9724746, EIA-0130864, and IIS-0002535
• Contributing students, staff, faculty Jodie Plumert Geb Thomas
David Schwebel Pete WillemsenPenney Nichols-Whitehead HongLing WangJennifer Lee Steffan MunteanuSarah Rains Joan Severson Sara Koschmeder Tom DrewesBen Fraga Forrest MeggersKim Schroeder Paul DebbinsStephanie Dawes Bohong ZhangLloyd Frei Zhi-hong WangKeith Miller Xiao-Qian Jiang
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