Do People Use the Shortest Path? Empirical Test of

Wardrop's First Principle

Shanjiang Zhu, Ph.D. Research ScientistDavid Levinson, Ph.D., Professor

Contact: zhuxx120@umd.eduUniversity of Maryland, College Park

Dept. of Civil and Environmental Engineering

TRB 2012, Washington D.C.

MotivationThe journey times in all routes actually used are equal and less than those which would be experienced by a single vehicle on any unused route.

Assumptions:

Equilibrium

Determinism

Perfect information

Utility maximization

Motivation:

I-35W Bridge Collapse MnPASS Program

Data Collection

Traffic and Behavioral Reactions

• Changing route and departure time are the most common reactions.

• I-35W replacement bridge does not save travel cost during all time periods as predicted by travel demand models.

Zhu, Shanjiang, David Levinson, Henry Liu and Kathleen Harder, (2010) The Traffic and Behavioral Effects of the I-35W Mississippi River Bridge Collapse, Transportation Research Part A: Policy and

Practice, 44(10).

Zhu, Shanjiang, David Levinson and Henry Liu, Measuring Winners and Losers from New I 35W Mississippi River Bridge, TRB DVD

#10-2298, January 2010, Washington DC

Implications for Travel Demand Modeling

• Revealing individual travel behavior

• Providing guidance for choice set generation

• Informing agent-based and individual-based travel demand models

GPS Data

(Source: Zhu and Levinson 2010a)

Route Matching under ArcGIS

Route Comparison under ArcGIS

(Source: Zhu and Levinson 2010a)

Do people use the shortest time path?

(Source: Zhu and Levinson 2010a)

Commute Trip vs. Non-Commute Trip

Commute Trip

Non-Commute Trip

(Source: Zhu and Levinson 2010a)

How Far is Traffic From User Equilibrium?

(Source: Zhu and Levinson 2010a)

Comparison between Commute Trip and Non-commute Trip

(Source: Zhu and Levinson 2010a)

Route Choice Set Generation Algorithms

•Link Labeling

•Link Elimination

•Link Penalty

•Simulation

Route Choice Set Generation Algorithms

•Link Labeling

•Link Elimination

•Link Penalty

•Simulation (67%)

Diversity in Commute Route

(Source: Zhu and Levinson 2010b)

Conclusions

• Majority of trips deviate from the shortest time path.

• Time gaps between shortest time paths and paths people actually use are smaller than 2 minutes for most people.

• None of the current choice set generation algorithms can generate all routes observed in the field.

• Simulation approach outperforms other alternatives.

Acknowledgments

• Sponsors: NSF, Oregon Transportation Research and Education Consortium, MnDOT, Metropolitan Consortium

BRIDGE: Behavioral Response to the I-35W Disruption: Gauging Equilibration (National Science Foundation) (Liu, Levinson, Harder)

Traffic Flow and Road User Impacts of the Collapse of the I-35W Bridge over the Mississippi River (MnDOT) (Levinson, Liu, Harder)

Value of Reliability (Oregon Transportation Research and Education Consortium) (Levinson, Harder)

• Colleagues: David Levinson, Henry Liu, Kathleen Harder, Shu Hong, Carlos Carrion

¿ Questions ?

Thank You

Shanjiang Zhu

Assistant Research ScientistUniversity of Maryland

Dept. of Civil & Environmental Engineeringzhuxx120@umd.edu