1、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 Divided into basic component behaviors In
2、tegrate all the basic components,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
3、behavior Vehicle leaves the current lane and enters an adjacent target lane,Behavior and Kinematics,Behavior sets control parameters Acceleration Driving curvature Kinematics moves a vehicle to a new position according to parameter values,Path,Path, a ribbon composed of road lanes and intersection c
4、orridors 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 simplifies behavior control Driving curvature determined by path Acceleration determined by behaviors Path
5、 provides a basis for spatial relationship,Cruising behavior,Determines desired speed Compare current speed with desired speed Current speed is higher, negative acceleration Current speed is lower, positive acceleration Proportional controllerReactive behavior Decision depends only on the state at t
6、his moment,Following behavior,Query the leader on the path of a vehicle Compute relative distance and relative speed Proportional-derivative controllerContribute the acceleration if negative, discard it if positive Reactive behavior,PD controller response to a slow leader,acceleration Before critica
7、l 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 leaders speed Keep a safe distance from its leader,Integration of cruising and following behaviors,If following acceleratio
8、n 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,What a vehicle does before entering an intersecti
9、on 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.),An intersection is a resource A vehicle should not ent
10、er it if it cant leave it soon Three sub behaviors because of different right-of-way rules Going straight Turning left Turning right,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
11、right on RED) Predicted gap (e.g., turning left on GREEN),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 a
12、cceleration controller,PD controller for stopping,Acceleration formulaPhases of vehicle actions No response Slow down and stop at desired position Stay stopped at desired position,PD controller for stopping,disadvantages No fully stopping, speed infinitely approaches 0 Acceleration value may be too
13、big, if critical point is missed,Invariant acceleration controller for stopping,ControllerAdvantages 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
14、 distance Conclusion: a better choice than PD controller,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
15、 is 0 END, stopping becomes impossible or is no longer necessary One state machine built for each sub behavior,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 requi
16、red 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,Simple right of way rules Problems: Deadlock Starvation Solutions
17、Deadlock breaking rule Starvation avoidance rule,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 inte
18、rsection acceleration In other phases, choose the former accelerationIntegrated 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,Modeled as a sequence of four steps Consider a la
19、ne 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,Consider DLC when the speed is belo
20、w 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,Move pursuit point from center of current lane to center of target lane
21、Use PD controller to control lateral moving of pursuit point Vehicle overshoots the target offset,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 changin
22、g to my target lane,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:
23、 too conservative Solution: 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,MLC is neces
24、sary The concept and structure of path dont 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 int
25、o 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,Acceleration combined contribution from Cruising behavior Following behavior Intersection behavior Driving curvature combined contribution from Path following Lane changing behavior,
