VRP - understanding [Capacities], [MaxOrderCount] and [PickupQuantity] attributes

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09-25-2016 10:58 PM
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New Contributor II

Hi,

I'm having a problem understanding the route generated by the Vehicle Routing Problem tool. Given the set of parameters I've entered, I'm expecting a different result.

I'm trying to generate a garbage waste pick-up route, starting from a Depot, to a series of neighborhood pickup points. I've loaded these points into the Orders list and I've entered assigned a field for the [PickupQuantities] property (the unit throughout is kilograms). Typically, the value for each stop i the field I've assigned is between roughly 500-1500 kg.

For the Routes list, I've added a truck (Truck_1) and added values to all the relevant fields. The main ones of interest/confusion right now is [Capacities] and [MaxOrderCount].

I understand [Capacities] is for how much the vehicle can carry. In my case, it's 8000 kg until full.

For [MaxOrderCount], I understand this to mean the maximum number of stops that my output route cannot exceed. In my case, I've entered 30 as this is the default and I'm happy with this because it's a number I don't think will be close to being reached or exceeded.

ESRI describes it like so:

             "The maximum allowable number of orders on the route. This field can't contain null values and has a default value of 30"

Other inputs: 

  • for Depots, I've loaded a list of points with relevant attributes assigned.
  • I have generated a basic road network, with time and distance attributes. I have not added any turn or time restrictions.

Here is my problem - I'm expecting the Solve output will;

  1. Generate a route starting at my nominated Depot for the truck
  2. The route will travel along the road network to the nearest stop(s) until up to 8000 kg have been picked up OR it has reached 30 stops. Given the rough average of kilograms per stop (500-1500 kg), I'm expecting the route will go to roughly 5-15 stops.
  3. Return to starting Depot.

What I am getting:

  1. the route starts at my nominated Depot for the truck
  2. The route travels along the road network until it reaches 30 stops, first going to a few nearby stops, then veering off to stops many kilometers away, despite closer stops.
  3. Returns to starting Depot

So, for some reason:

  • the [MaxOrderCount] attribute is forcing the route to go to the absolute number I've assigned to it. When i change it 10, it always goes to 10 stops. Change it 20, it goes to 20 stops. 
  • It is ignoring both the [Capacities] attribute of the truck and [PickupQuantity] attribute (that was assigned to a particular field when I initially set up the Orders list) 
  • The route is not going to next nearest available stops. As mentioned, my road network is without turn or time restrictions, so I don't know why it is veering way off to other stops when closer ones are available.

If anybody has any suggestions or questions that might help, please ask. I'm a novice user of Network Analyst and this is completely stumping me to the point I need help!

David

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New Contributor II

Correction: After some more testing and checking the results, I've realised that truck [Capacities] attribute and [PickupQuantity] attribute are not being ignored. What is still vexing me now is the [MaxOrderCount] defining how many stops to look for and go to. This I don't want - I want Network Analyst to decide the most efficient way to fill up the truck, and therefore, the number of stops.

Any thoughts or is my way of thinking about this problem flawed?

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Esri Contributor

Hi David,

How are you trying to solve this VRP Problem?  Using a VRP layer in ArcMap and inputting directly into the network analyst window?  Using a script with tables as the input?  Model Builder?  

Can you look at your results and see how much was loaded onto the truck when it picked up trash at 30 sites (If in the VRP layer depot visits should get you this value easily)?  Is it under the capacity of the vehicle, 8000 kg? 

From your description of the problem it sounds like the most number of stops a route should have is 16.  This would assume that each stop had the lowest value for pick up of 500 kg.  The solver is set up to stop when the vehicle is full if that happens before the max number of stops is reached, so I'd recommend examining the pickup quantities and the capacity to make sure they are what you are actually intending and the first step is to determine what the solver sees as a the amount picked up for the route.

Thanks,

Heather 

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New Contributor III

I second Heather's suggestion. I assume you are using a non-ordered pair, which I believe is correct. There must be a problem with the capacities of the vehicle and the pickup quantities of the order, because the solver will not exceed the route (vehicle) capacity. There is also a capacity count on the network layer too, but since you're only doing weight then this would be set to 1. I would check this out, but this is probably not the issue.

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