589: Designated Drivers

Explain xkcd: It's 'cause you're dumb.
Revision as of 17:43, 23 September 2022 by PoolloverNathan (talk | contribs) (specification)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search
Designated Drivers
Calling a cab means cutting into beer money.
Title text: Calling a cab means cutting into beer money.


When a group of people go together to any kind of event where they expect to drink alcohol, and would like to drive to and from the event, it is usual to select one who has to be the designated driver.[citation needed] This person will then stay sober during the event, and can thus safely drive the other people home afterwards disregarding how drunk the other people become.

However, as this comic points out, if it's not a simple task of going from A to B and back, all together at the same time, then it becomes a complex problem that requires an intricate kind of strategy and logical thinking to solve. And may need more than one driver.

In this comic Cueball addresses his friends, regarding this problem right before they enter a bar. It seems they have already decided that one of the friends will be the designated driver. But then Cueball mentions that they will have to leave in two groups. And for some reason one of these groups will need at least two drivers (this is hard to explain - see below under number of drivers.) So now they already need three designated drivers. Furthermore, someone has to go and pick up another friend. And also two of them have to leave earlier than the rest by 10:00.

In the third panel the situation seems to be illustrated. Three people are drawn outside the bar with three lines going to the bar, so the number of lines leaving and entering each destination seems to represent a person each. Since the number of people leaving and entering each destination is the same, this makes it seem like the diagram is intended to be accurate. There are four people entering and exiting the bar and six people entering and exiting both the party and the dinner. The confusing part of the diagram is that there are only three people at the bar to begin with, not the four shown in the first panel. It also seems strange that someone will go back to the bar and especially that another goes back to the dinner from the party. It is thus not easy to make the diagram fit the description. See below for a possible take on the chart.

But the general concept would be that some people meet at a bar before joining the rest of a group at dinner, then later most of these move on to a party. After the party (or bar/dinner) people are going to head home in different groups.

The enormous complexities of planning who car pools with whom, from where to where, and when, make an excellent logic puzzle. And what is worse, anyone who has to drive needs to stay sober. So it is important to solve the puzzle before the drinking starts, or else there will be too few that can drive, or too many who never get to drink.

To make matters worse Tom complicates this already complicated logical puzzle, by involving the classic logic puzzle of the wolf, goat and cabbage (sometimes also known as Fox-chicken-grain puzzle). In the last panel, the guy on the right is shown standing with a goat on a tether, saying he can't be in the car with the wolf. Cueball is then brought to swearing over this. (The goat puzzle was also the subject of 1134: Logic Boat and 2348: Boat Puzzle). And this may go some way of explaining why there needs to be a number of drivers.

The title text makes it clear why ordering a taxi is out of the question as it would take money out of the beer budget. Of course it also cost money to use your own car for gas etc. But when you already have a car, it is always cheaper to use that than pay for a taxi.

The chart[edit]

It's possible to match the chart up with the events in the comic if we assume two things: first, that everyone's initial position in the chart is at home, and second, that the party takes place at Cueball's house. Whether or not Randall intended it this way isn't certain.

For clarity, I'll be referring to the first cueball as Cueball, the second as David, Megan as Emily, and the third cueball as Tom.

  • Cueball leaves his house to meet Tom, David, and Emily at the bar.
    • When leaving the bar, Cueball returns home before dinner, possibly to set up for the party.
    • Emily leaves with either Tom or David to go to dinner while the other goes to pick up Paul.
  • At dinner Julia arrives from her house, Cueball arrives from his house, Emily arrives with either Tom or David from the bar, and Paul arrives with the person that didn't drive for Emily.
    • When leaving dinner, David has to be the one going home by himself as Emily and Julia will leave together, Tom has agreed to be a designated driver, Paul does not have a car, and Cueball is the host of the party.
    • The remaining five take three cars to Cueball's for the party. (Julia's car, Cueball's car, and Tom's car)
  • At 10:00 Julia will leave with Emily, and Tom will take Paul home once the party is over.

Number of drivers[edit]

Unless a more efficient solution exists, the minimum number of people that have to remain sober is three: Tom, David, and either Julia or Emily. Emily is able to begin drinking the earliest, starting at the bar and continuing the rest of the night. If the place everyone is having dinner at serves alcohol, Paul can begin drinking at dinner. If Emily elected to stay sober, Julia can start drinking when Paul does. Cueball is the last to be able to drink, only getting to start once everyone is at the party.

Interestingly enough, if the goat and wolf cannot drive, then they only make a difference if Paul has the wolf, in which case David would have to pick Paul up and take him home, and Tom and his goat would leave after dinner.

If either the wolf or the goat can drive, then a sober human driver is not needed for the vehicle in which that animal travels.


[Cueball is addressing three people outside a bar, indicated by a sign (two Cueball-like guys and Megan).]
Cueball: Wait, who's driving?
First Cueball-like guy: Why?
First Cueball-like guy: Tom, right?
[Zoom in on Cueball.]
Cueball: Yes, but we have to leave in two groups. One of which will need at least two drivers.
[There is text both above and below a flowchart with arrows between a group of the three people Cueball is talking to, and three houses that are labeled 'bar', 'dinner', and 'party'. Three lines point from the group of people to the bar and a fourth arrives from the party. Four lines points away from the bar. Two goes to the dinner one to the party and one away to the left. There are six arrows arriving at the dinner. Apart from the two lines coming from the bar, there is one long arrow pointing to the dinner from the left and two coming in from above. One more comes from the party below. Six arrows points away. One arrow goes away to the top right, the other five arrows points straight down to the party. There are also six arrows coming and leaving the party. Apart from the five from the dinner there was the one coming in from the bar. The six arrows leaving are the one arrow that went to the bar and the one to the dinner. The other four leaves in two groups of two, on straight down and two curving to the left.]
Cueball (off-panel): Someone has to get Paul, and Julia and Emily have to leave by 10:00.
Labels: Bar
Labels: Dinner
Labels: Party
Cueball (off-panel): The logistics of who can get drunk are nontrivial.
[The second Cueball-like guy to the right has an goat on a string behind him, which was not visible in the first panel, as he was at that time only partly inside the frame.]
Second Cueball-like guy: Yeah, and I can't ride in a car with the wolf because he'll eat my goat.
Cueball: Dammit, guys.

comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


I think I read a reference to the goat/wolf puzzle in an older comic. 18:08, 1 January 2014 (UTC)

Why no explanation of the third panel? Is it because it doesn't make sense? That seems unlike Randall, so I'll have a go.

Proposed Order of Events:

  • On the diagram, we see three figures entering the bar, and three lines entering dinner (probably Paul, and Emily and Julie). That makes six people altogether.
This makes no sense as there are four at the bar to begin with. Also one of the people already there would have to go and pick-up Paul and thus arrive at the party with him (two lines entering). Since Megan could be one of the two girls, the last girl could be the one arriving alone. But the above takes the first Cueball out of the equation! Thus if what I wrote here is true, then all the rest of this explanation below falls --Kynde (talk) 19:17, 31 October 2015 (UTC)
  • Of the three at the bar, two go to dinner and one goes straight to the party
  • All five people leave the dinner and go to the party, joining the sixth.
  • Two of the six leave the party together (Julie and Emily at 10pm)
  • One of the six leaves the party and goes back to the dinner venue, and from there goes home.
  • One of the six leaves the party and goes back to the bar
  • The last two leave the party and on their way home, appear to join up with the one who went back to the bar

Because there are no times or identities assigned to the paths, other interpretations are possible.


  • The diagram as a whole has six entries and six exits, as does each venue. There are definitely six people who all enter from the outside, and eventually leave.
  • Why are there four people visible in the first panel, but only three people start at the bar? That part makes no sense. To match the diagram to the comic, we have to pretend that there are only three people in the first panel.
  • Who is Tom? He must be one of the people visible in the first panel, even though he is spoken about as though he wasn't there.

Ignoring the goat for now, how many drivers do we need?

  • Most cars can take five people at a pinch, so sheer numbers don't seem to be the issue.
  • You need two drivers (and two cars) if people were leaving at different times, or heading in entirely different directions.
  • Presumably, Julie and Emily arrive in their own car and also leave in it. Ignore them for now..
  • Someone drives back from the party to the dinner, and then home. This must be one of the people from the first panel, and they must have their own car.


  • There are only three people at the bar, Tom, Megan and (I'll say) David. They each have their own car.
  • David drives to the party. Tom and Megan drive separately to the dinner, one of them collecting Paul on the way.
  • Tom and Megan drive from the dinner to the party; Paul rides with one of them.
  • Megan later drives back to the dinner venue, then home.
  • Paul later drives Tom's car back to the bar, and proceeds to get drunk.
  • David drives Tom a ride to the bar, to collect his car and drive Paul home.

Note that this scenario implies that everybody who is initially at the bar has to be a designated driver.

And I have still not considered the goat.

Any other interpretations would be welcome! I am not really satisfied with this but got tired of thinking about it. 18:52, 7 February 2014 (UTC)

tl;dr or Wikipedia:Too long; didn't read. Please calm down just to the essentials. And please try to keep an explain just straight forward. --Dgbrt (talk) 21:08, 7 February 2014 (UTC)
I have made a suggestion that could explain the information and the diagram, but it assumes that the party is held at Cueballs place (the one who talks first). And that he starts and ends there. The three drivers is though not easy to explain. --Kynde (talk) 19:17, 31 October 2015 (UTC)

<sigh> everyone forgets the cabbage... Brettpeirce (talk) 15:12, 27 February 2014 (UTC)

- For those unfamiliar, the goat/wolf reference is an old logic puzzle. You have a goat, wolf and head of cabbage. Using a rowboat, how can you get them all safely across a lake? Sometimes the assumptions are given: Goat eats cabbage, Wolf eats goat. Sometimes only 1 item at a time in rowboat, sometimes two. Solve. (Goat, empty, ...)

- BTW, I think the diagram description above is ok, shows how lots of interpretations possible. If it is inaccurate, well, has the artist already been to the bar? Arranging outings with friends, sometimes it's just a hassle, eh? And people will try to solve problems with the tools they know, hence a flow-diagram from the head XKCD geek. Just needs a state table with optimizations to make it complete! (-: 18:25, 9 June 2014 (UTC)

I like the double meaning of "non-trivial" in the comic. There's the math sense of the term and also the human sense. To fully appreciate the human sense it helps to be old enough to know that, say, 35 years ago, drunk driving was commonly regarded as a trivial problem. MADD (Mothers Against Drunk Driving), founded in 1980, helped change this, as did increasingly drastic penalties and public shaming of people who drove drunk. When I was growing up (1960s) and a young adult (1970s) there was no concept of Designated Driver. Npsych (talk) 09:52, 9 October 2015 (UTC)

I believe the reason one group needs two drivers is that said group may be due for a longer, cross-continental trip (and driving hung over with minimal sleep in a sedan isn't much easier than driving drunk)... Maybe we finally solved anothe logic problem? Papayaman1000 (talk) 03:22, 6 March 2016 (UTC)

Just overhauled the last two sections. If anyone has anything to add or I made a mistake in my solution, I'd love to hear feedback on it. Toadfart (talk) 21:46, 14 September 2016 (UTC)