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Erstellt / Aktualisiert 20.06.2021 / 10.08.2022
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Fenster schliessen

User equilibrium vs. System optimum

User equilibrium (UE): Find a feasible assignment in which all used paths have equal and minimal travel times.

  • This principle follows directy from the assumptions that:
    • drivers choose minimum time paths
    • drivers are well-informed about network conditions
  • most widely used trip assignment method for auto trips
  • UE does not minimize congestion
  • Total system travel time may not be the minimum

 

System optimum (SO): Find a feasible assignment which minimizes the total system travel time.

  • SO is not a natural process --> measures have to be taken to reach SO

 

Fenster schliessen

Dynamic Traffic Assignment (DTA)

DTA must involve the following concepts:

  • A model for how congestion (travel times) varies over time
  • A concept of equilibrium route choice
  • Equilibration based on experienced travel times, not instantaneous travel times

Compared to Static Traffic Assignment (STA) DTA-Simulations are more realistic.

Problems:

  • Limited link capacity (high computing cost)
  • multicommodity flow (e.g. trucks, toll roads)
  • elastic demand
  • multi-mode supply
Fenster schliessen

Calibration of microscopic models

Three step strategy:

  • Capacity calibration
  • Route choice calibration
  • System performance calibration

Calibration Process:

  • Select parameters to calibrate
    • Global
    • Link specific
  • Collect field data
  • Set calibration goals
  • Search for optimal parameter values
Fenster schliessen

Microsimulation - Operational outputs

Operational outputs specifications

  • link level demand
  • speed
  • density
  • throughput
  • delay
  • post processing data
  • queues
  • travel time
  • 2D, 3D visualization
Fenster schliessen

ALINEA

ALINEA is a local feedback ramp-metering strategy.

Fenster schliessen

Behavioral differences - AVs vs. human drivers

  • Human drivers anticipate disturbances downstream
    --> inability of traffic anticipation can lead to platoon instability
  • AVs drive with lower speed variations at stable following conditions
  • Reaction times of humans are larger than of controllers (yet comparable)
  • Controllers drive based on time headway strategies but humans don't

Such behavioral differences directly impact traffic congestion, energy consumption, driving behaviors and possibly other dimensions.