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Wednesday, September 5, 2012

Drive-through lane pipelining and parallelization

I've noticed something interesting about the drive through lane at In-n-Out. For those who aren't from the left coast (or that one specific place in Texas, apparently), it's a local burger chain with something of a cult following and a "secret menu".

It seems that whenever they get backed up, someone will grab a wireless ordering device, throw on a headset, and will start walking back down the line of cars. In this way, they can start cooking the orders for cars which are nowhere near the ordering board. They probably also reduce the number of round-trips required to get an entire order added to their systems by virtue of removing the "yell at a board and hope they hear you" audio situation.

It occurs to me that this is a good way to clear out the backlog. Everything they do is "just in time", so the sooner an order is placed, the sooner it can be handled. If there is some blockage which is keeping cars from getting to the order board to get their orders started, then the problem will cascade backwards. On the one hand, not being able to pull up to the board to order means no more orders can swamp the kitchen, but it also means added wait times for anyone who bothers to stay in line.

If this actually works, then all of the new orders start coming up, and that backlog can be drained relatively quickly. Once cars are able to reach the board, order, and pull past to let another car order, there's no reason to have someone out there doing that job. They can go back inside and rejoin the rotation.

I don't think I've seen any other drive through place which does anything of the sort during periods of peak load and higher delay. If this was something involving software, I'd think the other places were passing on this technique due to patents. However, since this is the realm of burger flipping, do they have the same lawsuit-happy stranglers of innovation running around?

The only other things I've seen used in an attempt to increase throughput are to double up on delivery windows. I think I saw a restaurant once that actually used both sides of its business as drive through takeout windows. This required some careful routing of lanes to keep things from gridlocking.

Also, there are places in Texas which have two DT lanes in parallel. How does the second one work, you ask? That's easy. You put your payment in a little tray and put a rock on top. Then it goes up, over, and down while making a fantastic metallic racket. It is replaced by your food, drinks, and change. The tray itself travels in such a way that it remains flat the whole time even though it is moving up, over, and down again.

You didn't think they used pneumatic tubes like bank drive throughs, did you? That only works for burritos.