Whether you call them fast food joints or "quick service restaurants," the underlying concept is the same: speed. So why, in an age when everything else is getting faster, are drive-thru wait times getting longer?

This is according to QSR Magazine's annual Drive-Thru Performance Study, which looks at speed, accuracy and other metrics from 2,188 different visits to 1,606 different fast food outlets representing 23 fast food brands.

According to the latest data, the average overall wait time is around 220 second (3 minutes, 40 seconds). Burger chains (204 seconds) were the least slow, followed by chicken chains (216 seconds), with sandwich shops bringing up the rear, coming in just a hair shy of 4 minutes.

Sandwich shops — which include Subway, Arby's Jimmy John's, and others — also tended to have the most cars waiting, at an average of 2.2, while chicken chains had only 1.01 vehicles sitting on line at a time.

The disparity between the types of menus makes some sense, in that burger joints likely have fewer customers asking for special orders and a roster of popular menu items that can be made quickly and easily. Chicken chains like KFC and Popeyes often have the food already made; it just needs to be packaged up per the customer's request. But sandwich shops are the most likely place to have customers making special requests, dragging down service times.

But why are times in general so slow — and getting slower?

It may be a matter of more limited time offers and premium items being added to menus. These products often take longer to make. Additionally, having so many items on a menu makes it harder for a kitchen to streamline production.

Taco Bell's Chief Operating Officer says the array of new menu items is altering the way the industry looks at service.

"It's not really that we're changing the service; it's how we accustom our mindsets to say that not everything is going to be a Doritos Locos Taco that you deliver in the restaurant," he explains to QSR Magazine. "There are going to be more complex products coming in, and we just have to change our training methods, our engagement plans in the restaurant, and how we approach them so that we can execute and still be relatively at a good speed that customers are going to be comfortable with."

So when's the best time of day to hit the drive-thru?

One good time might be in the morning, when the industry average drops below 3 minutes (175 seconds), even though there are an average of 1.94 cars in line at a time. This is probably because most breakfast menus are made up of a smaller number of items with a handful of very popular items dominating the orders.

But the fastest time to race through the drive-thru is actually between lunch and dinner. This "Snack" daypart averages a little more than a second faster than breakfast and had virtually the same number of cars in line (1.98).

"The piece that surprised me more than anything was the mid-afternoon snack," says QSR Magazine's Brian Baker. "It's equally busy to the other dayparts and they're just killing it on time. You would expect for lunch and breakfast, you would have your No. 1 best employees in place, shoes shined, ready to roll, and in the middle of the afternoon you relax and catch your breath. But I look at this and say, it's just as busy in the middle of the day as it is for dinner or lunch or breakfast, and they are even faster."

Our guess is that this speed is due to relatively light in-store business, meaning the kitchen isn't trying to do double-duty with a busy drive-thru line and customers waiting for food at the counter.

One thing that was really interesting about the study was the apparent inefficacy of presell menu boards — the smaller displays that you see before you get to the big board where you place your order. These are intended to help the customer make up his/her mind before getting to the ordering point, but they don't seem to be having much effect on service times.

In fact, service times at restaurants with presell boards were often slower than at those without. At burger chains with these presell menus, the average time was 197 seconds, compared to 189 seconds without them.

The difference was even more pronounced at chicken chains, where the average wait time for a restaurant with a presell board was 238 seconds, nearly 45 seconds longer than at those without the advance menu listings.

The only place where presells seemed to make a difference was at sandwich shops, where the 220 second average for stores with presell boards beat out those without presells by 26 seconds.