Last December, I posted an article asking whether double drive-thru's were more efficient. There was some good discussion on it at the time (before I switched to Facebook comments) and the general consensus was that yes, they can actually work pretty well.
Recently, I found myself with a hotel room overlooking one such drive-through at McDonald's. Some people ask for ocean views, but I digress. This gave me a good opportunity to watch the cars move through the two lanes and see if there were any issues with their merging. So I video-recorded about 15 minutes of hot drive-thru action and present the following frame grabs for your reading pleasure:
Things start out with dark car 1 in the right lane and white car 2 in the left lane. This is gonna get long, so click the Read More link to see all the pics...
The right lane empties first, then the left. Of course, as you will see below, there is no guarantee that it will always work in this order. I have to assume that the length of time it takes to place an order is the deciding factor.
We're still right-then-left, with cars 3 and 4 sliding in behind 1 and 2.
A little traffic jam formed with cars 4 and 5, but, miraculously, they still stay in order.
6 follows 5, and then 7 pulls up. 7 was actually at the speaker before 6. This leads me to think the guys working the speakers have some way of switching back and forth automatically. Note this is the only point in the sequence where there was a single line of cars entering the drive-thru, meaning drivers needed to decide upon left or right as they filtered in. Let's watch that black pickup and big SUV at the end of the line.
The black pickup goes left, the SUV goes right. As for everyone else, look at that, like a beautiful ballet. Still in order.
This is where it might've gotten interesting. Had I kept recording, we could say that the truck is 12, the little car in the right speaker is 13 and the SUV will be 14. But what happens if someone else comes up behind and fills the empty slot on the left after the big black pickup? Note, all along, the odds have been on the right and the evens on the left. I was just counting them as they came up to the speaker. Assuming that SUV is the last car, the order would be left-right-right. No big earth-shaking revelation, but an interesting exercise. The moral of the story would seem to be that you should always favor the shorter line, even if there seems to be a pattern in front of you.