Multiple legs of network analysis?

[TomKearns]

I am interested in solving a problem in which the cost of transportation changes at (as of yet unselected) depots and is then transported to a final destination.  Say I have cows spread all over and they are shipped at a higher cost to processing plants (depots) and then shipped to a distributor at a lowered cost (final destination).  My depots would be selected from cities and the final destination would be chosen from a shorter list of larger cities.

I have a few questions. 

1. Is there a built in function within network analyst to do this?
2. If not, is there a seprate script which makes this possible / where can I search for additional scripts?

3.  Would the best plan of attack to be the selection of the final destination points and then building toward toward the depots which would then be used to define the coverage area.

Or define the depots from the coverage area first and then attempt to select the final destination?  My worry with the latter is that non of the larger cities will actually be optimal when the other depots could be altered to correct it.

Thanks in advance,

Tom

[RobertGarrity]

Hi Tom,

It looks like you may be able to use the Location-Allocation solver, or the VRP solver. It depends on your objective...
Do you want to plan routes for drivers on a day-to-day basis, or do you want to figure out how to allocate cattle to processing centers, perhaps due to production-capacity constraints or for strategic planning on where to place processing/distributing centers?

If it's for day-to-day routing, you could use the VRP solver. Otherwise, you could use the Location-Allocation solver. My understanding, but I'm not confident I understand correctly, is you need Location-Allocation. If that's right, you could divide the problem into two parts: the first solve would be to choose processing plant locations (load ranches/farms/feedlots as demand points and processing plants as facilities), the second solve would be to choose distributor locations (load processing plants as demand points and distributors as facilities).

Can you please elaborate on the problem a little more so I, or someone else, can try to provide a better response?

Thanks,
Robert

[TomKearns]

Thanks for the reply. 

I believe I will be using the Location allocation first, as opposed to the VRP, due to the fact that I have not decided where the facilities or depots will be placed.  Once this is decided I will use the VRP to set the correct route for the movement of the units. 

To better restate my initial question, I am looking to place a final destination facility or two somewhere in the North West which would be fed by units coming from depots.  These depots would be fed from the general areas surrounding them but would be at a higher transportation cost than that of the depot to final facility transportation cost.

Like you mentioned, I think the steps required would be to select the final destination site and use Location allocation to define my depot sites.  I would then run another location allocation in order to show the coverage area these depots reach.

I guess my problem was that I was trying to do two problems with one allocation.  Now the problem is that I am having trouble selecting which direction to approach the problem from, large to small or small to large.