Meaning of the FIRST THRU NODE header

[chrhansk]

As mentioned in #29: There is a simple relationship between nodes and zones, that is, a zone is a node. You mention regarding the FIRST THRU NODE property:

An important one is the . In the some networks (like Sioux-Falls) it is equal to 1, indicating that traffic can move through all nodes, including zones. In other networks when traffic is not allow to go through zones, the zones are numbered 1 to n and the is set to n+1.

This suggests the following to me: If FIRST THRU NODE = 1, ignore the property, otherwise: The zones 1, ..., n are forbidden, which is to say that no traffic may pass through them. I would assume that this implies that no path of edges in any of the trips is allowed to touch any of the nodes 1,...,n.

Now I looked at the Anaheim net file, which specifies the FIRST THRU NODE to be 39, implying that no traffc may pass through nodes 1,...,38.

The problem is that all trips in the corresponding [trip file](https://github.com/bstabler/TransportationNetworks/blob/would mean that any path has to contain nodes 1,..., 38.

I therefore think that the FIRST THRU NODE excludes nodes from being contained in a path except for the origin / destination of the path, hence the THRU name. So paths can contain forbidden nodes as long as they connect them.

Is this a correct understanding of the FIRST THRU NODE entry?

[chkwon]

It concurs with my understanding.

I think those 'non-thru nodes' represent the center of residential/commercial blocks, while all other 'thru nodes' represent physical intersection of roads.

[chrhansk]

Thanks, I appreciate the help