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Behavior Control of Virtual Vehicle. Hongling Wang April 21, 2003. Introduction. Purpose of behavior control Run a virtual vehicle on a road network Following traffic rules A vehicle should be able to get anywhere in the road network Behavior control is complex

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behavior control of virtual vehicle

Behavior Control of Virtual Vehicle

Hongling Wang

April 21, 2003

introduction
Introduction
  • Purpose of behavior control
    • Run a virtual vehicle on a road network
    • Following traffic rules
    • A vehicle should be able to get anywhere in the road network
  • Behavior control is complex
    • Divided into basic component behaviors
    • Integrate all the basic components
components of vehicle behavior
Components of Vehicle Behavior
  • Cruising behavior
    • Vehicle drives at desired speed
  • Following behavior
    • Vehicle keeps a safe distance behind its leader
  • Intersection behavior
    • Vehicle traverses intersections safely
      • Obeys traffic signals
      • Respects right of way
  • Lane changing behavior
    • Vehicle leaves the current lane and enters an adjacent target lane
behavior and kinematics
Behavior and Kinematics
  • Behavior sets control parameters
    • Acceleration
    • Driving curvature
  • Kinematics moves a vehicle to a new position according to parameter values
slide5
Path
  • Path, a ribbon composed of road lanes and intersection corridors
  • Path used to guide vehicle moving
    • Path forms a consistent frame of reference
    • Pursuit point on path centerline
  • Path is an interface between a vehicle and outside world
path cont
Path (Cont.)
  • Path simplifies behavior control
    • Driving curvature determined by path
    • Acceleration determined by behaviors
  • Path provides a basis for spatial relationship
cruising behavior
Cruising behavior
  • Determines desired speed
  • Compare current speed with desired speed
    • Current speed is higher, negative acceleration
    • Current speed is lower, positive acceleration
  • Proportional controller
  • Reactive behavior
    • Decision depends only on the state at this moment
following behavior
Following behavior
  • Query the leader on the path of a vehicle
  • Compute relative distance and relative speed
  • Proportional-derivative controller
  • Contribute the acceleration if negative, discard it if positive
  • Reactive behavior
pd controller response to a slow leader
PD controller response to a slow leader
  • acceleration
    • Before critical point, positive
    • After critical point, negative and increasing
    • After negative maximum, negative and decreasing to approach 0
  • phases of vehicle actions
    • No response
    • Slow down to leader’s speed
    • Keep a safe distance from its leader
integration of cruising and following behaviors
Integration of cruising and following behaviors
  • If following acceleration >0, choose cruising acceleration
  • If following acceleration <=0, choose smaller value among the two
  • Integrated behavior: a vehicle always tries to drive at a desired speed, while keeps from running into or too close to its leader
intersection behavior
Intersection behavior
  • What a vehicle does before entering an intersection
    • Stop
    • Keep going
    • Stop and go alternatively
  • Actions chosen according to ambient traffic and traffic control signals
  • Sequential behavior
    • Decision depends on both the state in last moment and the state in this moment
intersection behavior cont
Intersection behavior (Cont.)
  • An intersection is a resource
    • A vehicle should not enter it if it can’t leave it soon
  • Three sub behaviors because of different right-of-way rules
    • Going straight
    • Turning left
    • Turning right
intersection behavior cont1
Intersection behavior (Cont.)
  • Main problems
    • Stop a vehicle on desired position
    • Using state machines to control action flow
    • Gap acceptance
      • Immediate gap (e.g., turning right on RED)
      • Predicted gap (e.g., turning left on GREEN)
stopping behavior
Stopping behavior
  • Requirements
    • Inform a vehicle it is the time to decelerate
    • Stop a vehicle in desired position if computed acceleration applied
    • Keep a vehicle stopped after it stopped
  • Acceleration computation method
    • PD controller
    • Invariant acceleration controller
pd controller for stopping
PD controller for stopping
  • Acceleration formula
  • Phases of vehicle actions
    • No response
    • Slow down and stop at desired position
    • Stay stopped at desired position
pd controller for stopping1
PD controller for stopping
  • disadvantages
    • No fully stopping, speed infinitely approaches 0
    • Acceleration value may be too big, if critical point is missed
invariant acceleration controller for stopping
Invariant acceleration controller for stopping
  • Controller
  • Advantages
    • Be able to give a full stop at desired position
    • Gives a reasonable acceleration in some cases where PD controller gives a too big acceleration
  • Disadvantage
    • Sensitive to small errors of both speed and distance
  • Conclusion: a better choice than PD controller
state machines for intersection behavior
State machines for Intersection behavior
  • Basic states of state machines for intersection behavior
    • START, no response to state of control signal
    • CONTINUE, keep going while stopping still possible
    • SLOWDOWN, decelerate for stopping
    • STOPPED, speed is 0
    • END, stopping becomes impossible or is no longer necessary
  • One state machine built for each sub behavior
gap acceptance computation
Gap acceptance computation
  • Gap is a time period within which my required space is free
    • A resource
    • Relationship between time and space
  • Immediate gap
    • Estimate when others will get to my required space
    • Check if it is within the gap
  • Predicted gap
    • Estimate when I will get to and leave my required space
    • Estimate when others will get to my required space
    • Check if they overlay
intersection behavior by simple right of way rules
Intersection behavior by simple right of way rules
  • Simple right of way rules
  • Problems:
    • Deadlock
    • Starvation
  • Solutions
    • Deadlock breaking rule
    • Starvation avoidance rule
integration of cruising following and intersection behaviors
Integration of cruising, following and intersection behaviors
  • Before intersection behavior is activated, choose the former acceleration
  • After it is activated
    • In SLOWDOWN or STOPPED phase, choose the smaller value among the former acceleration and intersection acceleration
    • In other phases, choose the former acceleration
  • Integrated behavior: A vehicle tries to drive at a desired speed, keeps a safe distance with its leader and responds to traffic control signals on intersections
lane change behavior
Lane change behavior
  • Modeled as a sequence of four steps
    • Consider a lane change
    • Choice of a target lane
    • Gap acceptance
    • Move over to the target lane
  • Classified as MLC and DLC
    • MLC, mandatory lane change
    • DLC, discretionary lane change
  • Sequential behavior
    • State machine with 4 states corresponding to the 4 steps
discretionary lane change
Discretionary Lane Change
  • Consider DLC when the speed is below a desired speed
  • Change to a neighboring lane for opportunity to increase speed
  • A gap is acceptable when both lead and lag gaps on target lane are acceptable
trajectories of a vehicle and its pursuit point during lane changing
Trajectories of a vehicle and its pursuit point during lane changing
  • Move pursuit point from center of current lane to center of target lane
  • Use PD controller to control lateral moving of pursuit point
  • Vehicle overshoots the target offset
gap acceptance for lane change
Gap acceptance for lane change
  • Both lead gap and lag gap are acceptable
  • My current leader and follower are not changing to my target lane
  • No vehicle on another adjacent lane of my target lane is changing to my target lane
integrate lane change behavior with following behavior
Integrate lane change behavior with following behavior
  • The concept of following leader changed
    • The ahead vehicle in my current lane
    • The ahead vehicle in my target lane if I am in lane change
    • The ahead vehicle whose target lane is my current lane and who is in lane change
  • Problem: too conservative
  • Solution: visibility computation
visibility computation
Visibility computation
  • The ahead vehicle in my current lane may be out of my way when I am in lane change
  • Lane change will complete sooner with visibility computation, especial when ahead vehicle is very slow
take mlc into consideration
Take MLC into consideration
  • MLC is necessary
  • The concept and structure of path don’t support MLC efficiently
  • Route, a higher level conceptual structure, is necessary for MLC
    • Route of a vehicle is composed of roads
  • Relation between route and path
    • Route is a long term plan
    • Path is a short term plane
    • Path is built to follow route
take mlc into consideration1
Take MLC into consideration
  • A multiple-lane MLC is treated as multiple single-lane changes
  • When still far from road end, consider only DLC, not MLC
  • DLC consistent with target of MLC is given priority
  • DLC against target of MLC is given some penalty for resource requirement
general behavior integration
General Behavior Integration
  • Acceleration combined contribution from
    • Cruising behavior
    • Following behavior
    • Intersection behavior
  • Driving curvature combined contribution from
    • Path following
    • Lane changing behavior