Oversaturated Freeway Flow Algorithm Next Generation Simulation Oversaturated Freeway Flow Algorithm Alexander Skabardonis, Hwasoo Yeo University of California, Berkeley NGSIM Team Meeting Washington DC January 21, 2007

Outline Problem Statement Oversaturated freeway flow model Car-following model Lane changing model Estimation of Parameters Car-following parameters Lane changing parameters Implementation Algorithm implementation Verification Validation

Problem Statement Existing Simulation Approaches Do not accurately model oversaturated traffic conditions such as repeated stops and starts, increased lane changes to position onto perceived “moving” lanes, or in the presence of tall vehicles, and large vehicle headways Use additional rules and parameters to the basic “desired headway” and “gap-acceptance” based car-following and lane changing models Introduce a large number of parameters that generally cannot be readily observed in the field

Project Overview Objectives: Develop an improved model for oversaturated freeway flow Focus on both car-following and lane-changing behaviors during congested conditions Evaluation of Model for “non-oversaturated” Flow Predict when & how non-oversaturated conditions breakdown Coordination Completed and ongoing NGSIM algorithms Software Developers Stakeholder participation in expert panels

Car-following: Concept Vehicle will change speed according to the current spacing sjam s v 1/t speed spacing vf v sjam t Alternative Distance form

Car-following base model concept -acceleration case xCF(t+dt)=xLeader(t+dt- t)-sjam Leader v, speed v2 vf CF s2 v1 v2 s1 v1 Acceleration s, spacing s1 s2

Car-following base model concept -deceleration case xCF(t+dt)=xLeader(t+dt- t)-sjam v, speed vf v2 Deceleration s2 v1 s1 v1 v2 s2 s1 s, spacing

Car-following Model Newell’s simplified CF model Maximum Acc Jam Spacing Wave travel time Newell’s simplified CF model Maximum Acc Free Flow speed Safety Constraint Maximum Dec

Lane Changing Model Lane changing choice model Gap acceptance model Mandatory Lane changing Entry, exit Discretionary lane changing Gap acceptance model Lane changing mechanism Lane changing Lane changing with cooperation Emergency Lane changing Lead gap Lane changing Vehicle n Lag gap n+1′ cooperation vehicles

Lane changing choice model (1) Mandatory lane changing Applied to turning and exit traffic Emergency Lane changing lExit T0 Exit location En Desired location in exit lane Number of lane changes needed Tn Stopping distance

Lane changing choice model(2) Discretionary Lane Changing Lane changing probability is the function of speed difference Probability that vehicle n at time t moves from lane l to lane l’ Ф : sensitivity to speed change

Gap acceptance conditions Lead gap condition Lead gap (Minimum gap condition) n Lag gap (Safety condition) Lag gap condition (Minimum gap condition) n+1′ (Safety condition)

Lane Changing Mechanism (1) Car-following rule for Lane changing pending x=MIN( xCF(Leader) , xCF(Veh Down) ) x= xCF(Leader) Try to pass and find next gap upstream vehicle downstream vehicle Veh up Veh down LC Leader Request Cooperation Conflict point

Lane Changing Mechanism (2) Car-following rule for cooperating vehicle x=MIN( xCF(Leader) , xCF(LC) ) End cooperation upstream vehicle Veh up Leader Coop LC Request Cooperation Conflict point

Lane Changing conflict If there exist conflict in lane changing x=MIN( xCF(Leader) , xCF(Veh Down) ) LC1 will yield to LC2 else x= xCF(Leader) LC2 will pass LC1 upstream vehicle LC downstream vehicle Veh up LC2 LC1 Leader Request Cooperation

On-Ramp Model – conflict zone

On-Ramp Model Conflict Zone x=MIN( xCF(Leader) , xCF(Veh Down) ) Find a downstream vehicle Veh down Leader Conflict point

Short Gap Mode (optional) Lane changing cooperation vehicles keep short gap before and after lane change Applied to Lane Changing or Cooperation vehicles Ends when the leader vehicle starts acceleration v, speed Leader Short gap mode Short gap mode s, spacing

Short gap mode

Effects of Short Gap (Relaxation) Merging area

Parameter Estimation Car-following Parameters Lane Changing Parameters vf : free-flow speed gjam : jam gap t: wave travel time au, al : Maximum acceleration and deceleration Lane Changing Parameters Ф: sensitivity to speed difference T : slope of lane changing for exit lane change E: target location in the exit lane for exit lane change mn: perceived HOV activation time Find starting times of vehicles exiting HOV

Free Flow Speed Extract from detector data 5min detector data 30sec detector data

Jam gap g= xn-1-ln-1-xn Jam gap Minimum gap at jam condition vehicle speed <3km/hr

Wave Travel Time t: time between the action of leader vehicle and the following vehicle 150 200 250 300 350 400 450 500 -2 2 4 6 8 10 12 14 t time(sec) Speed(ft/sec) Acc(ft/sec2)

Wave Speed Wave speed = sjam / t = (ㅣ+gjam) / t US101 I-80 Mean=18.07km/hr,11.22miles/hr I-80 Mean=19.59km/hr,12.18miles/hr

Max Acceleration & Deceleration Extracted from NGSIM trajectories data US101 Passenger cars (n=4163) Mean=4.516(m/s2), std= 0.808 mean= -4.398(m/s2), std=0.827

Sensitivity to speed difference(φ) in discretionary lane changing Assume constant φ Probability of LC

Exit Lane Changing Parameters (E and T) Exit location

Parameters - Car-following (1)

Parameters - Car-following (2)

Parameters – Lane Changing

Algorithm Implementation (1) Mode? Car-following Lane Changing Cooperating Change Mode Car-following for Cooperating Gap Acceptable? Yes No Change lane Lane Changing? Emergency Lane Changing? Yes Yes Car-following rule No Maximum deceleration No Change Mode to CF Find cooperating vehicle and set mode Car-following rule Change mode of the cooperating vehicle to CF Car-following for lane changing pending End

Algorithm Implementation (2) AIMSUN SDK Replacing AIMSUN car-following and lane changing model Programming language: C++ A2VehicleBehavioralModel A2Vehicle A2VehicleModelTestCreator A2VehicleBehavioralModelTest A2VehicleTest dll entry point for new model Car-following and lane changing Logic Vehicle behaviors

Algorithm Verification – US101

Algorithm Verification: Exit Lane Changing

Model Testing I-80 (1) Simulation 2:30PM-3:00PM Detector 7

Model Testing I-80 (2)

Characteristics of the Proposed Algorithm Consistent with kinematic wave theory Parameters Physical meaning observable Microscopic: wave travel time, jam gap, free flow speed, Max Acc, Dec Macroscopic: wave travel time, jam density, free flow speed Can be used for model calibration Mechanism Oriented approach Integrated Algorithm with Car-following and Lane changing

Next Steps Complete Model Validation Software Code & Documentation Trajectory data Aggregate data Software Code & Documentation Final Report

Possible Future Enhancements Relaxation Process Partially implemented Caused by driver characteristic change Sampling interval for speed change Jam gap, reaction time Traffic Hysteresis Caused by asymmetric behavior Oscillations in speed-spacing Not considered Asymmetry model

Components of the suggested algorithm Oversaturated Freeway flow algorithm Car-following Lane changing LC Choice model Base Car-following Coop Car-following Car-following for Conflict Cooperation choice Forced LC choice CF model before LC LC pending Car-following LC Target choice Gap Acceptance LC Car-following Apply LC model After LC Car-following CF model after LC Emergency LC Car-following `