589: Designated Drivers

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
Designated Drivers
Calling a cab means cutting into beer money.
Title text: Calling a cab means cutting into beer money.

[edit] Explanation

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. 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 becomes.

However, as this comic points out, if it not a simple task of going from A to B and back, all together at the same time, then it becomes an 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, (Megan and two other Cueball-like guys), regarding this problem right before they enter a bar. It seems they have already decided that one of the friends (Tom) 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 Paul. (This could be one of the designated drivers though). And also two girls (Julia and Emily) has to leave earlier than the rest by 10:00. (That could then be be one of the two groups that Cueball mentions, and then one of these girls should drive).

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 two many who never gets to drink.

To make matters worse the last Cueball-like guy complicates this already complicated logical puzzle, by involving the classic logic puzzle of the wolf, goat and cabbage. In the last panel the guy is shown standing with a goat on a teeter, 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). This must mean that one of the people who has yet to arrive comes with a wolf. And this may go some way of explaining why there needs to be a [[number of drivers]. But since it did not seem like Cueball was thinking about this fact when he mentioned this, that cannot be the explanation.

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.

[edit] The chart

Since the first panel must take place before any drinking takes place, to make the title of the comic make sense, then there is already missing one from the bar, since we know that there are four at the bar at the start of the comic. To make the diagram fit the fourth person should then be the one coming from the party. But he would thus come from there before anyone else arrived at the party. And then someone will have to leave directly from the bar without going to the dinner or party, since no one will come back later. And since Julia and Emily leaves together, this cannot be either of them. That would also mean that only five leaves the party since one of the leaving arrows was the fourth to get to the bar early. And there are six arriving, all of which must be assumed to arrive later yet. And since no one enters the party from outside, someone must have been at the party site from the start and would stay there afterwards.

All this will at first make very little sense, so in the end it does not seems likely that the diagram in any way can represent the situation precisely. Except if the party is thrown by one of the guys, and he starts and finishes there. Her below is a possible explanation that would explain all the information and the chart. It this was at all intended to be possible by Randall is not certain but it fits:

  • The three people outside the bar are the one represented on the diagram.
    • Two Cueball-like guys of which the last one is Tom, the designated driver, and Megan represents one of the girls mentioned later Emily or Julia.
    • They arrive together to the bar.
  • Here they meet Cueball.
    • It is Cueball who throws the party. So the party is at his place, and he has arrived at the bar from there.
    • There is thus no arrow entering the party for him to begin with, as he lives there.
  • There are now four at the bar.
    • Later Cueball will take a route past his house (the party place) before going to the dinner.
    • Two of the other three in the bar will go straight to the place of the dinner.
    • The last in the bar is the one who has to go after Paul. He thus leaves the chart.
  • The guy who picked up Paul will return together with him to the dinner as the two arrows coming in from the top.
  • The second girl (apart from Megan) is the last long arrow coming in alone from the right.
  • Now all six people are at the dinner.
    • After the dinner one of these six people (a guy) will leave alone
    • The other five including Cueball will continue to the party at his house.
  • There are thus five at the party but only four of these leaves afterwards in two groups of two.
    • Two of these are the girls that leaves already at 10:00 leaving only three guys in the house.
    • When the two last leave Cueball will stay at home, thus explaining why only four leaves.

[edit] Number of drivers

The chart offers no solution to the puzzle of why a single group would need more than one driver. As neither of the groups leaving the party is more than two people it would be hard to get more than two drivers. And hard to explain why there would be need for more than one.

The only time more than two lines are following each other from one place is the three that arrives together at the bar and the five that moves from dinner to party. And even five people can normally fit in one car.

Of course when we begin to take into account that one of them has a goat and one of the others have a wolf, then there are suddenly eight living beings that needs transport. And this may explain the need for two cars. But still not the more than one driver for a single car.

[edit] Transcript

[Cueball is addressing three people outside a bar (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! ⋅ 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)
Personal tools


It seems you are using noscript, which is stopping our project wonderful ads from working. Explain xkcd uses ads to pay for bandwidth, and we manually approve all our advertisers, and our ads are restricted to unobtrusive images and slow animated GIFs. If you found this site helpful, please consider whitelisting us.

Want to advertise with us, or donate to us with Paypal?