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5.4 AccelerationParameterDefinition
smart-fm edited this page Nov 9, 2018
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SimMobility ST has simple structures to save most of the parameters used in the previous models, using a structured XML file to save all used parameters.
This section defines threshold for car-following model (CF) accelerations used in Section 5.3.
<!-- A. ACCELERATION MODELS -->
<!-- A.1. CAR FOLLOWING PARAMETERS-->
<param name="min_response_distance" value="5.0"/>
<!-- Car following parameters alpha beta gama lambda rho stddev-->
<param name="CF_parameters_1" value="0.0400 0.7220 0.2420 0.6820 0.6000 0.8250"/>
<param name="CF_parameters_2" value=" -0.0418 0.0000 0.1510 0.6840 0.6800 0.8020"/>
For the target gap acceleration model, the parameters are defined with the name target_gap_acc_param in Section 5.2
<!-- A.2. TARGET GAP ACCELERATION PARAMETERS
accFWDGap = [2] * (Desired position FWD) ^ [3] * exp( [4] * DeltaV+ ) * exp( [5] * DeltaV-) + N(0,[6]²)
accBCKGap = [7] * (Desired position BCK) ^ [8] * exp( [9] * DeltaV+ ) * exp( [10] * DeltaV-) + N(0,[11]²)
accFWDGap = [12] * (Desired position ADJ) + N(0,[13]²)
The desired position is given by:
Desired position FWD = LeadHeadway + leadlenght + [1] * FWDgap
Desired position BCK = LagHeadway + length + laglength + ( 1- [1] ) * BCKgap
Desired position ADJ = [1] * ADJgap + length - LagHeadway
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] -->
<param name="target_gap_acc_parm" value="
0.604 0.385 0.323 0.0678 0.217 0.583 -0.596 -0.219 0.0832 0.170 1.478 0.131 0.300"/>
This section defines threshold for the acceleration models.
<!--A.3. ACCELERATION THRESHOLDS-->
<!--MAIN TABLES (m/s2)
Each column represents the following speed bins (m/s) defined in "speed_scaler" below
Each row represents a vehicle class
NOTE: The code needs to be changed to accept a variable number of vehicle classes -->
<!-- Maximum acceleration -->
<param name="max_acc_car1" value="3.05 2.40 1.70 1.21 0.90"/>
<!-- Normal deceleration -->
<param name="normal_deceleration_car1" value="2.40 2.00 1.41 1.44 1.47"/>
<!-- Maximum deceleration -->
<param name="max_deceleration_car1" value="4.80 4.35 3.90 3.30 3.00"/>
<!-- VARIATION TABLES (factor)-->
<!-- Each column represents the following population percentile
0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95 -->
<param name="max_acceleration_scale" value=
"0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50"/>
<param name="normal_deceleration_scale" value=
"1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00"/>
<param name="max_deceleration_scale" value=
"1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00"/>
<!-- GENERAL FACTORS for TRESHOLDS (factor)-->
<!-- number of bins | first bin | bin size
Example: "5 10 5" is equal to [0-10,10-15,15-20,20-25,25-]-->
<param name="speed_scaler" value="5 10 5"/>
<!-- Grade factor -->
<param name="acceleration_grade_factor" value="0.305"/>
<!-- Default grade (m/m) -->
<param name="tmp_all_grades" value="0"/>
This section defines the headway thresholds distribution (in Section 5.3)
<!-- B. HEADWAY THRESHOLDS -->
<param name="hbuffer_lower" value="2.2352"/>
<!-- Variation (factor)-->
<!-- Each column represents the following population percentile
0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95 -->
<param name="hbuffer_Upper" value=" 1.7498 2.2737 2.5871 2.8379 3.0633 3.2814 3.5068 3.7578 4.0718 4.5979"/>
This section defines parameters of the acceleration when approaching a traffic light (see Section 5.2)
<!-- C. TRAFFIC LIGHT RESPONSE -->
<param name="min_response_distance" value="5.0"/>
<param name="yellow_stop_headway" value="1.0"/>
<param name="min_speed_yellow" value="2.2352"/>
This section defines the reaction distribution parameters (see Section 4)
<!-- D. UPDATE STEP SIZE (REACTION TIME RELATED)
Driver behavior (e.g. responses to stimuli) is updated periodically during simulation depending on the state of the vehicle (i.e. depending on whether the vehicle is decelerating, accelerating, traveling at uniform speed, or is stopped). At each call of the function updateStepSize (i.e. at the end of each decision instant) a new update state size is drawn from a truncated log-normal (normal?) distribution (seconds):
mean stdev lower upper perception(%) -->
<param name="dec_update_step_size" value= "0.5 0.0 0.5 0.5 0.5"/>
<param name="acc_update_step_size" value= "1.0 0.0 1.0 1.0 0.5"/>
<param name="uniform_speed_update_step_size" value= "1.0 0.0 1.0 1.0 0.5"/>
<param name="stopped_vehicle_update_step_size" value= "0.5 0.0 0.5 0.5 0.5"/>
This section defines the desired speed distribution (see Section 5.3)
<!-- F. DESIRED SPEED
The desired speed constrained by the posted speed limit is defined by
Vdesired = speed_factor * Vsign * ( 1 + Vvar) -->
<param name="speed_factor" value="2.2352"/>
<!-- Vvar is read from the table bellow -->
<!-- Each column represents the following population percentile
0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95 -->
<param name="speed_limit_add_on" value=" -0.1911 -0.0708 -0.0082 0.0397 0.0810 0.1248 0.1661 0.2180 0.2745 0.3657"/>
This section defines the visibility distribution parameters:
<!-- G. VISIBILITY
NOTE (Carlos): The structure of the visibility is not a mature one -> Needs work
The visibility_distance parameter is used in the car follow model to reduce the follower reaction time when subject vehicle brakes (in meter) -->
<param name="visibility_distance" value="10"/>