Have you noticed that many of the new fast food restaurants have 2 drive-thru lanes. My first experience with one I thought “wow, really?”. I found myself frozen with confusion. My wife saved me by pointing to the left lane. Similar to choosing a restaurant or a movie, I now can blame her if the car behind me gets the food first.
My car reached the ordering sign. I am terrible at ordering fast food. Even though I drive 99% of the time, my wife will lean over me and shout the order through my window. There are just too many details my over-indulged kids care about that the make the process too complicated. Have you ever communicated the perfect order only to be replied with “sir, can you repeat that?”. AHHH.
To my surprise, I noticed all cars converge on a single “pay” window. 2 lanes should be faster than one, right? I thought it would be interesting to model the typical fast food drive-thru process comparing 1 versus 2 lanes.
The poll results and comments are very interesting. Most people feel 2 lanes versus 1 makes no difference but not all agree. This validates why I wanted to build a simple model and see what I could learn. I created this model to have fun and encourage readers to not take the results too seriously. I do think the model is a great start to an iterative approach of building a much more complex drive thru model though. You learn a lot in building a process model and I have come to appreciate the subtle details necessary to fully model a drive thru.
Here is a video of me running the model and comparing 2 lane versus 1 lane on average time to get your food.
Inputs and Assumptions
My goal was to see how quickly I could capture the general flow of a drive thru and only add details as needed. The model is data driven and a user can easily change the following:
|Number Of Lanes||2|
|Order Time In Seconds||U(30,15)|
|Percent Pay By Cash||50%|
|Pay By Credit Card Seconds||U(15,5)|
|Pay By Cash Seconds||U(30,5)|
|Pull Ahead Threshold Seconds||45|
|Pick Up Food In Seconds||U(15,5)|
|Vehicle Arrival Frequency Minutes||E(1)|
|Vehicle Arrival Quantity||1|
Certainly this list is not exhaustive, but I feel representative of the types of things that determine a drive-thru’s process performance. Just to get reasonable defaults I recorded my wait times through various fast food drive-thrus. I also recorded other driver’s times while I was there. Anyone know if drive thru times are publicly available?
I used a Google Map image of a real drive-thru and the distances are to scale to accurately model the impact of vehicle length. The vehicles move 1 mph as they move though the drive-thru queue.
When picking up the food, if the model determines it will take greater than 45 seconds, the car is told to pull ahead and not block the vehicles behind them.
Potential Next Iteration
Even with black boxing the “Get Food” window with a simple, single time distribution, 2 lanes ended up being faster. Had this not been true, I was planning on modeling what specific items a driver orders. I would actually model the kitchen area and the cooking of that restaurant’s menu of items. Drivers would have to wait for their specific ordered items to actually be cooked and ready.
Check Out Dan’s Blog – “Dan’s Green Shoes”: