Aurora RNM - trip assignment

Hi all,

I have spent some time studying implementing trip assignment module to Aurora. I have also studied the current software architecture of Aurora for this purpose. I have summarized some notes, including the modifications (see Part C) that I would suggest to do.

Please comment and let me know if there is anything you would like me to elaborate...

I will also upload some numerical calculations to the Aurora Blog later ...

A. Use of trip assignment in Aurora:

1. Interaction between travel demand and traffic condition

-E.g. choice between freeway and arterial

- No congestion -> everyone goes for freeway

- Freeway congested -> Someone may choose to take arterial

- Question: what is the proportion of flow on freeway/arterial?

- Some numerical calculations will be given later …

2. Estimate demand changes with respect to control policies (e.g. ramp metering, toll, traffic information provision etc..)

B. Assignment principles (travel demand model):

1. ‘ad-hoc’

- e.g. assign traffic to the shortest path at the current time interval

2. Deterministic user equilibrium (DUE)

- Ideal (actual)

- Instantaneous

3. Stochastic user equilibrium (SUE)

4. Stochastic ‘learning’ process / Dynamic game

- Evolution of drivers’ behavior as a result of ‘learning’

- system gradually would converge to some steady state (a Nash equilibrium) if there is no ‘disruption’ to the system …

Methods 1, 2, and 3 have been studied and used in the literature.

Personally I would buy Method 4. It seems to be more ‘statistically’ oriented. PeMS should be useful for calibrating or validating this.

C. Things need to be added to current Aurora RNM:

1. Split ratio profile over time

- the split ratios also supposed to be ‘state-dependent’

2. Data storage for

- flow on different paths;

- flow heading to different destination;

- different kind of vehicles (e.g. HOV vs LOV; Trucks vs autos).

3. Path travel time calculation

The path travel time in Aurora is currently calculated in an ‘instantaneous’ fashion: In other words, it is assumed that the travel time along the whole path does not vary after the driver enters the path. This doesn’t seem to be realistic ..