Simulating a Sobriety Checkpoint

[ced]

Hi,
am working on simulating a sobriety checkpoint with arena and i have read a lot of papers and some few books but i still haven't found the kind of information needed to do this though i think its a pretty simple and straight forward project.
I found an example of a car wash model which looked similar only that i want to have more than one officer and in their case they had one machine.I believe i have to implement this in my process and that is hard for me to do since i had no knowledge about simulation at all. For now this is what i have acheived: Create(car arrival or Queue) -Process (Officer) where am using the seize,delay release action-Dispose. and am able to run though i want to get a curve where having a certain number of officers lined up wouldn't make any difference and also that having a certain number of officers will not improve the effectiveness of the checkpoint since the officer at A always has to be open for vehicles to be released to officer B and/or C and D since they are all in a line.
Any help will be greatly appreciated, thanks a lot

[ewilliams]

First consider which of the following descriptions is correct:
1. The driver stops only once. A police officer checks the driver (e.g., for sobriety). There are multiple officers, and they are interchangeable.
2. The driver stops several times for slightly different checks (e.g., one for slurred speech, one for contraband, etc.). Each checkpoint has a dedicated group of officers (e.g., an officer who checks sobriety cannot check for contraband, or vice versa).
3. The driver stops several times for slightly different checks (e.g., one for slurred speech, one for contraband, etc.). All the checkpoints share a group (presumably larger) of officers -- i.e., any officer can work at any checkpoint.
If #1 is right, define one resource Officer with multiple units and use it at one Process [Seize-Delay-Release] module.
If #2 is right, define multiple resources OfficerType1, OfficerType2, etc., with multiple units of each, and use each at a succession of Process blocks.
If #3 is right, define one resource Officer with (quite a few) multiple units and a succession of Process blocks, at each of which an Officer is "seized".
Further questions on this thread (or others!) welcome.

[ced]

ewilliams,
Description 1 is correct and i have the one process set-up for one officer,but what do you mean by defining one officer with multiple units? Does that mean i keep the one process and include the number of officers in there or add other processes as other officers, and how would i account for the scenario whereby if officer 1 has a vehicle and officers 2 and 3 are empty they have to wait for officer 1 to release his vehicle before they can have vehicles through to them, thank you once again.

[ewilliams]

In the Resource block of the Basic Process template, you can define Resource capacity (the number of officers). In the Process module, use Seize-Delay-Release and seize 1 officer. Arriving cars will seize one officer each; if all are seized, the car will wait in the Process module for the next officer freed.

[ced]

I have been able to set my sobriety checkpoint up in the right way but my results makes it seem like the officers are stopping vehicles at the same time and am not sure but if am interpreting my results correctly i think it seems as if every vehicle is stopped by all the officers though its not suppose to be like that because once you are stopped by one officer you are ok to go if you are cleared.My results gives the same efficiency and values for all my officers.Any suggestions or ideas. Or that is what am suppose to be getting?

[ewilliams]

From the original description, I assumed that Officer Jones could have Vehicle #1 stopped during a time interval overlapping the time interval during which Officer Smith had Vehicle #2 stopped. Is this true?
Assuming it is true, quite OK to have multiple vehicles stopped at once. What is not OK, given this follow-up question, is to have one vehicle stopped more than one time. If you have more than one Process (Seize-Delay-Release) block in the model to represent an officer stopping a driver, ask yourself "Why?". I visualize using only one such block. If you really need more than one such block, give each Vehicle an Attribute which represents (0 = this vehicle has not been stopped before; 1 = it has been stopped already by an officer). If the attribute is equal to 1, set the stopping (delay time) at the next Process block (again, if you even need such a block) equal to 0.

[ced]

Yes that is true, Officer jones could have vehicle 1 stopped during a time interval overlapping the time during which officer smith had a vehicle stopped. But when officer jones has a vehicle stopped and Officer smith releases a vehicles no vehicle can come to him until officer jones releases his vehicle and the next vehicle in line goes t Officer smith.And am assuming this is taken into account by arena at least the waiting part.And i did use one process and set officers 1 and 2 in there and the results for both of them are the same. If there is a way i can attach the result in here i will so you take a look at it it with the two officers, thanks

[ewilliams]

Aha! Now I expand my visualization of your situation -- I infer that the vehicles are in a long single line (one-lane road)? Let us suppose the vehicles that may be stopped are going east. Officer Jones is west of Officer Smith. If Officer Smith releases a vehicle, another vehicle cannot come from the queue until Officer Jones's checkpoint is physically cleared. Now, is this expanded visualization of mine correct? If it is, the segments of roads are resources which must be "seized" and can be used by only one vehicle at a time, and this aspect of the situation needs insertion into the model. You can do this with no more actual Resources (in the Arena sense) by using Hold and Signal blocks. If you haven't used those blocks yet, they are well worth examining and learning.

[ced]

I think that is what i need, i could not find it on my student version of Arena 10.Am not sure if its not on there or i just can't find them.

[ewilliams]

These blocks (Hold and Signal) are in my student version I use for teaching, but well concealed. Go to File/Template Panel/Attach. Attach the Advanced Process template. The blocks there may be connected freely with the blocks in the Basic Process template, which is probably the template with which you are most familiar.