ODME

DTA System Update: ODME for Link Counts and VMT Deviation Penalty

In this update, we enhance the system with two additional penalty terms in the modified generalized equilibrium condition. The first term addresses the link count deviation, and the second focuses on the total system-wide VMT deviation:

1. Link Count Penalty: Applies to both physical links (with actual operations) and virtual links, which simulate OD pairs.
2. VMT Penalty: Applied exclusively to physical links.

To accommodate these changes, we’ve introduced network modifications, including the addition of O2D virtual links. These virtual links allow for slightly longer travel times and hold additional demand, which enables dynamic traffic assignment (DTA). Using the generalized link cost function, this implementation also supports simultaneous ODME.

Key Improvements:

• Network Constraints: We’ve formulated the system as a constraint-capacitated user equilibrium, adding constraints for total link count deviation and VMT deviation.

• Route File Outputs: The system now supports route file generation at the end of traffic link-based assignments, avoiding internal column generation or updates, which optimizes computational time.

• Warm Start Feature: The system allows for the preloading of demand and link volumes, enabling quicker convergence to equilibrium. Initial gaps of 1–2% can be reached within a few iterations, significantly speeding up the process.

  • Base Demand: A new feature that allows for preloaded demand and volumes, which accelerates the warm start process and reduces the time spent on iterations.

Performance:

• Tested on the Chicago regional network (1,778zones, 12,982 nodes).
• Average speed: ~2 seconds per iteration.

User Actions Required:

1. Modify settings in setting.csv for the ODME mode flag and VMT/link count observation flags.
2. Populate link.csv with observed link volumes.
3. Define base demand for each mode type in the demand file.
4. Set base volumes in the link volume file for a warm start.

Output Enhancements:

• The assignment results include performance metrics and are post-processed for fast output. This update also includes a new QVF output to capture peak-to-load factors and congestion duration data P, and time-dependent speed for analysis period.

This release ensures faster computational speed, stable user equilibrium, and improved peak-hour analysis, consistent with the system's advancements over the past two years.