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!