Hi Alex,
I have started building an assignment solver for Aurora RNM. At this preliminary stage, I constructed a simple network with two parallel links (as attached in the email):
Link 1001: origin link
Link 1002: one of the parallel links connecting nodes 1 and 2
Link 1003: one of the parallel links connecting nodes 1 and 2
Link 1004: destination link
The demand profile can be seen in the xml file.
The network is uncongested, which can be verified by seeing no delay on any link in it after simulation. I have the following problems:
1. Since the network is uncongested, I don't understand why the inflow to link 1002 from the origin link 1001 is distorted.
2. How can I split some flow from the origin to route 2 (i.e. via Link 1003). Currently all the flow from the origin is flowing on route 1 (i.e. Link 1002).
Please advise. Please let me know if you want more information from me.
Andy
P.S. For other people, please let me know if you want to have the config file of the 2-link network that we discussed above...
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5 comments:
Alex's response:
Andy,
1. Everything looks fine.
Flow1002 does not repeat Flow1001 exactly because it takes time for link 1002 to accumulate the vehicles.
2. Make split ratios on Node 1, say, '0.7, 0.3' instead of '1.0, 0.0'.
Alex.
Thanks, Alex,
I will try 'point 2' later.
On 'point 1', indeed I have observed the same thing when I worked on the signal controller.
Is such 'flow-distortion' an intended feature built in Aurora RNM? Is it something related to the 'equilibrium / non-equilibrium' state that being mentioned in your paper: 'qualitative theory of CTM'?
In fact. it seems a bit strange to me as this's not quite the CTM (and the queuing theory) that I know. As far as I understand, in uncongested state in CTM, the outflow profile should be simply the same as the inflow, only with a state-independent time shift (the time-shift is supposed to be the free flow travel time)...
It's not aurora, it is CTM.
Make the duration of the nonzero demand longer and you'll see how Flow1002 will reach this equilibrium value.
Then, when you abruptly turn the demand off, it'll take some time for the link 1002 to get rid of all te vehicles. So, Flow1002 will _gradually_ decline.
I guess the outflow will be usually smoother than the inflow especially if there is a big change (such as discontinuity) in the inflow.
Andy, the flow propagation equation by Astarita (1996) should readily explain this:
v(t+\tau(t)) = u(t)/[1+d\tau(t)/dt]
especially when travel time \tau is increasing.
- Jeff
Hi Jeff,
Yes, I understand what you said and I observe this kind of 'outflow spreading' in whole-link travel time model (e.g. Friesz's (1993) model).
However, I didn't expect to see this in CTM, which is an 'outflow traffic model'...
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