Dynamic Traffic Modeling: Applications and Frontiers

Stephen BoylesAssistant Professor

Civil, Architectural & Environmental EngineeringThe University of Texas at Austin

April 23, 2014CTR Symposium

Austin, TX

A question to start…

Construction work will restrict capacity on a major route for an extended period of time. Should traffic signals be retimed?

IT DEPENDS!!!

Some relevant factors to consider:

1. How long is the closure?2. What is the capacity reduction?3. What alternate routes exist?4. What signals can you control?5. What about impacts on other traffic?6. How much data do you have available?7. How much information will travelers have?

and so on…

Many of these factors can be grouped into two categories:

“Supply” side

Lane closuresSpeed limit changes

Changes in signal timing

“Demand” side

Diversion ratesTraveler informationSensitivity to delay

How large should the study area be?

On the one hand, focusing on a small area or corridor allows you to

use more realistic simulators.

On the other hand, projects can have impacts far

beyond the immediate area.

Microscopic models simulate a small area.

Mesoscopic models strike a balance.

Macroscopic models simulate a large area.

Realism

Supply-side Demand-sideDynamictraffic

assignment

Talk outline:

1. Brief background on dynamic traffic assignment2. Applications of DTA3. Current research frontiers

BACKGROUND

Supply and demand are dependent on each other.

In traffic assignment models, we find a mutually consistentsolution in which drivers’ decisions are consistent with the traffic conditions they expect. (Often called equilibrium.)

Supply: Traffic flow model

Demand: Route choice model

Path choicesDeparture times

CongestionTravel times

An example

The top route is long, but uncongested. The bottom route is shorter, but has limited capacity.

An example

After drivers gain experience, some will choose the top route, and some will choose the bottom, in a way that the travel times are roughly equal.

An example

When capacity is added to the bottom route, drivers will divert from the top route to the bottom. This diversion would continue until the travel times were equal again… there is no improvement in travel times.

What makes DTA “dynamic”?

The traffic flow model is simpler than CORSIM or VISSIM, but still tracks queue buildup and dissipation, signal delays, etc. and can be applied on a regional scale.

APPLICATIONS

Work zone impacts

• Traffic Control Plans (TCPs) are used to coordinate phasing of roadway construction projects

• DTA models have been demonstrated to effectively identify impacts due to construction projects/TCP scenarios

– Provide traffic control– Identify roadway realignments, lane closures,

and detours

Subnetworks

?

Scenarios

• A combination of network modifications varying with respect to modification scope were used to assess 54 impact scenarios

• Three locations: Guadalupe Street, 15th Street, and 7th

Street• Three different sized

subnetworks within the downtown Austin network: Connected order of 5, 7, and 9

• Five Real-world Scenarios

Subnetwork Size Evaluation: Recommendations

Emissions modeling with MOVES

Dynamic models provide enough detail for emissions models, while still feasible to run on large, regional scales.

FRONTIERS

Making model calibration easier

Making model calibration easier

Integration with activity-based models

Shopping

Kid’s School

Home WorkRestaurant

7:15 AM

7:30 AM 7:35 AM

8:00 AM 12:30 PM12:35 PM

1:00 PM1:05PM5:00 PM

5:30 PM

6:00 PM

6:30 PM

Drive Drive

DriveDrive

Walk

Walk

Autonomous vehicles

Autonomous vehicles

Autonomous vehicles

Conclusions• DTA can integrate human behavior into traffic modeling.

Conclusions• DTA can integrate human behavior into traffic modeling.• It has applications in many areas requiring realistic traffic

estimates over large regions.

Conclusions• DTA can integrate human behavior into traffic modeling.• It has applications in many areas requiring realistic traffic

estimates over large regions.• The future is bright in traffic assignment!