OD Demand matrix units

[Evangelos Paschalidis]

Hi everyone,

I have managed to successfully install AequilibraE, set up my network, nodes, zones, etc. and everything seems to be working fine, but I have a rather basic question.

What are the units of the OD demand matrix that I should provide? Is it trips/day, trips/h etc.? It has not been clear to me from the documentation even though I suspect trips/h.

Thanks!

Evangelos

[Jamie Cook]

Evangelos, 

That is indeed a bit of assumed industry knowledge there - Demand matrices can represent trips for any period that you (the modeller) desire. They could be hourly demand or daily demand or the demand for a 3 hour AM peak. 

The crucial thing is that when assigning demand matrices that the resulting volume aligns with the capacity column in your network (ie. the field that is specified via the set_capacity_field method). Generally, I believe that people use a capacity in veh/hr so normally would transform any demand matrices into a trips per hr equivalent before assigning. 

- Jamie 

http://jamiecook.wordpress.com

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[Evangelos Paschalidis]

Thank you very much for the response Jamie. This is very useful and simplifies things.

However, could you please let me know though where  the  set_capacity_field method is? I am not able to find it within the traffic assignment toolbox (I am using QGIS).

In any case, maybe this is less important. As an approximation, I could compute the theoretical capacity of my network by summing the capacity of all links manually.

Thanks,

Evangelos

[Pedro Camargo]

Hey Evangelos,

Jamie is referring to the Python method used to set the capacity field, which is called under the hood when you set it in the QGIS plugin.

This sentence worries me, though.

"I could compute the theoretical capacity of my network by summing the capacity of all links manually."

What would that mean?

Cheers,

Pedro

---- On Mon, 24 Mar 2025 18:01:46 +1000 Evangelos Paschalidis <evpa...@gmail.com> wrote ---

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[Evangelos Paschalidis]

Hi Pedro,

Thanks for joining the conversation, much appreciated.

I see now why I did not know about the  set_capacity_field feature.

Regarding your comment, you are right, we are talking about flows (and not vehicles), so what I had in mind was wrong.

I am planning to go with Jamie's advice and transform my data into veh/hr, but any other feedback is welcome :)

Best,

Evangelos