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Project P resentation 

ForECIV 748 – Traffic Flow Theory

  ESTIMATING PARAMETERS FOR

MODIFIED GREENSHIELD’S MODEL

FROM FIELD OBSERVATIONS  

Omor Sharif

F a l l 2 0 1 0

U n i v e r s i t y o f S o u t h C a r o l i n a , C o l u m b i a

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Topics

1. Background and Objective

2. Data Extraction

3. Data Visualization

4. Parameter Estimation of Modified’ Greenshield’s Model

5. Findings and Conclusions

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Background and Project Objective

To associate theoretical traffic models with field observations of traffic flow

•Greenshield’s Model (1934) – Linear Speed-Density Model

•Modified Greenshield’s Model – To improve upon limitations of original model

•Two Regime Model adopted in this project–

•Estimating parameters foro Constant Speed Model (Free flow Regime)o Modified Greenshield’s Model (Congested Regime )

Theoretical Traffic Stream Models

Single Regime Models

Multi-regime Models

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Data Extraction

Source - Online Database Repositories

GPS-enabled vehicles and mobile devices, traditional road sensors,fixed point sensors and GPS probes

Two Sources - 1. INRIX.com2. TRAFFIC.com

Dataset available from TRAFFIC.com

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D a t a V i s u a l i z a t i o n - M a c ro s c o p i c F l o w C h a ra c t e r i s t i c s ( @ H a m m o n d R o a d )

FIGURE Hourly flow patterns for different days in EB direction

FIGURE Hourly flow patterns for different days in WB direction

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D a t a V i s u a l i z a t i o n - M a c ro s c o p i c F l o w C h a ra c t e r i s t i c s ( @ H a m m o n d R o a d )

FIGURE Directional Split on Thursday

FIGURE Average hourly distribution of mode in the study period

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D a t a V i s u a l i z a t i o n - M a c ro s c o p i c S p e e d C h a ra c t e r i s t i c s ( @ H a m m o n d R o a d )

FIGURE Hourly speed distributions with standard deviation (WB)

FIGURE Speed histogram from four week speed data (EB)

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Estimating Parameters

Greenshield’s model:

Two Regime Model:

Modified Greenshield’s model:

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Pa ra m e t e r s f o r I - 4 0 @ H a m m o n d Ro a d

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Pa ra m e t e r s f o r I - 4 0 @ H a r r i s o n Ave n u e

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Pa ra m e t e r s f o r I - 4 0 @ D av i s D r ive

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Closing RemarksTwo regime model is preferable instead of a single regime Constant speed model for free flow region and Modified Greenshield’s model for congested flow region was adoptedThe fit is better for Hammond road and Davis drive compared to Harrison avenue The free flow speed is lower than speed limit for all three sectionsMode overestimates Jam density for Hammond Road and Davis drive (reaches maximum possible physical density)At a density greater than 40 pce/mile/lane all sections reaches capacity and become congested at higher densityVery few observations at capacity and poor tracking of near capacity observations by the modelOverall The proposed two regime model tracks the field data reasonably well

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T h a n k Yo u

Q u e s t i o n s ?