vinayak dixit

Value of Time of Carshare Users in SydneyRevealed Preference Study of GPS Data

Dr. V.V. Dixit | John Trieu | Sisi Jian | Xun Li

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Introduction – Why Study Value of Time?

• Economic cost of congestion– $3.9 billion to Sydney in 2005

(BITRE, 2007)

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This Study – Value of Time in Sydney

• Goal– Value of time for motorists in Sydney

• Why?– Important consideration in Congestion Charging

schemes– Important input to Cost-Benefit Analysis of

transport projects• Economic “benefit” of travel time savings

• How?– Revealed preference study of GPS data– Data provided by carshare program in Sydney

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Value of Travel Time Savings (1)

• Value of Time– Not directly measurable– Minimum travel time, regardless of mode and

route

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Value of Travel Time Savings (2)

• Need to consider the “Value of Travel Time Savings”

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What is a Revealed Preference study?

• Collection of raw data (e.g. GPS logs)• Convert data to trips• Determine relationships between trip

decisions and factors influencing choices

• The preferences of drivers are “Revealed”– Preferences are not explicitly “Stated” by drivers

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Past Studies

• Different locations = Different characteristics– Los Angeles– Brisbane

• Stated Preference = Controlled Experiment(Hensher, Greene and Li, 2011)– Artificial environment

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Delineating Trips – Overview

• GPS Logs = Data Points– Need trips

• Trip Identification – Trip Ends– (1) Time between GPS data points– (2) Time with zero movement– (3) Significant changes in direction

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Delineating Trips – (1) Time between GPS data points

• Large amount of time (e.g. 2 Days)– Trip has ended

• Cut-off = 20 minutes– Timeout of in-car GPS units

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Delineating Trips – (2) Time with zero movement

• Based upon maximum signal cycle time in Sydney – 150 seconds during peak periods

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Delineating Trips – (3) Significant changes in direction

• U-turns• Turns greater than 90 degrees– Sensitivity testing undertaken on the

change in heading– No change in number of trips identified

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This Study

• Focal Point– Toll Road versus Untolled Alternative– Can isolate value of time• Explicit cost for toll road• Stochastic travel time saving

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Study Area (1) – M2 vs Epping Road

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Study Area (2) – M4 vs Parramatta Road

• Used as a “control” for the study– Equivalent to “no treatment” scenario in

experiments

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This Study

• Other variables / covariates– Age / Experience– Preferred Travel Mode– Car Ownership

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Modelling – Value of Expected Travel Time Savings

• Regression Modelling– Binary Logit Model

Choice of Motorway or Arterial• Value of Expected Travel Time Savings (VETTS)– $9.63 / hour

• Comparison VETTS– Los Angeles, USA: $21.46 / hour– Brisbane, Australia: $17.60 / hour

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Modelling – Value of Expected Travel Time Savings

• Value of Expected Travel Time Savings (VETTS)– $9.63 / hour

• VETTS result is more than 50% less than in other cities

• Reason for difference– VETTS identified is specific to Carshare Users– Carshare Users are suspected of having lower

VETTS compared to average motorist• Cannot be used as a representative sample group

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Further Studies

• Risk aversion– Travel times are stochastic– Need to include risk parameter• Model including risk parameter is ongoing

– Risk models considered:• Constant Absolute Risk Aversion (CARA)• Constant Relative Risk Aversion (CRRA)

• Ongoing / Not yet finalised

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Questions?