faq 107824175

How to understand traffic assignment?

by Xinru Wang on 2017-02-12 05:20:38

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Now I understand all agents choose one plan according to scores in each iteration. But what I get confused about is that:

1.Do all agents choose a plan at first and get assigned to the network, then finished the iteration. Or for example, agents with activities in first 15 minutes are assigned to the network, and then the next 15-min agents reroute based on the network condition, choose their plan...so on.

2. Is dynamic routing included in default replanning module, or should be self-defined? If it is included in the default system, do agents rerouting every 15 minutes or at each node?

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Comments: 1

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Re: How to understand traffic assignment?

by Johan W. Joubert on 2017-02-13 06:08:16

Xinru, maybe others in the community can/should add their voices, but here's my answer.

1. All agents choose an initial plan, yes. The essence of MATSim is that it is a multi-agent system. And one of the characteristics is that there is no assignment being done by some outside process. There rather is a notion of autonomous decision-making (the way agent-bassed models should work). Agents 'figure it out by themselves'. That is, they just try and follow their chosen plan. If the plan dictates that the agent should leave home at 06:58, then the agent leaves that activity at that time. The route, if not available, is calculated using the shortest path Dijkstra (or whatever the non-default you choose). The agent then traverses the network strictly according to the calculated route... whether there is congestion or not. MATSim is a continuous system (there is a time-step variable that can be set, but it is buried pretty deeply, I guess for a reason.
2. Not on by default. Rerouting (if switched on as a replanning strategy) only occurs at the end of an iteration, and only if the agent is chosen for replanning. There is within-day-replanning, but for that I have to refer you to Chapter 30 of the MATSim book.