# question

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## FIFO in a patient waiting line

In the attached model, the behavior in a waiting line is not FIFO as expected. A woman arrives first in the waiting line but takes the 2nd position. Then a man arrives later and takes the 1st position in the waiting line. Why is the behavior not FIFO by default ?

FlexSim HC 5.0.12

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It is FIFO, but it's based on who first "acquires" a spot in the line and not who first arrives at the line. Patients in HC don't start walking to a location until they've acquired a spot for themselves in the location they're walking to.

In your model, the man arrives first, acquires the first spot, and then begins walking the long distance between the arrival object and the waiting line. The woman arrives while the man is in the middle of his walk, acquires the second spot, walks to the waiting line, and arrives first at the waiting line since she had a shorter distance to walk. She waits at the second spot since that's the one she acquired.

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@Matthew Gillespie , as a consequence, even if people are placed in the waiting line by "FIFO based on spot acquirement", is it nonetheless possible to make the person who arrived first in the waiting line (the woman) to go to the podium first (before the man) ? Just like in waiting lines in real life ? The issue is that if a patient is coming from a distant area, the patient flow is stopped in the waiting line until his arrival, sometimes for long enough to distort statistics.

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Eloïse Martin ·

This usually isn't an issue since the arrival rate is usually much greater than the travel time. If this becomes an issue in your model you'd need to somehow shorten the distance the patients need to travel. You could do that by putting another waiting line just in front of the actual waiting line. Here's an example model for that.

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