2841: Sign Combo

Explain xkcd: It's 'cause you're dumb.
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Sign Combo
Speed Limit: 45 MPH / Minimum: 65 MPH
Title text: Speed Limit: 45 MPH / Minimum: 65 MPH


This comic depicts a trio of road signs that provide legal instructions that are, in combination, impossible to follow: "Do not enter" precludes passing the point of the sign, the No U-Turn sign precludes turning around, and the "No Stopping Any Time" sign precludes both halting before the sign as well as reversing back (even ignoring that this is usually already illegal with or without signs explicitly forbidding it). A driver approaching this sign combo would seemingly be forced to violate at least one of the three, probably leading to the caption's concern expressed as "Oh no".

Of the three, "No U-Turn" is the one with the largest wiggle room, as it can be defined more narrowly/specifically as driving in a U-shape; thus, a driver might be able to get around it by drawing a more elaborate path. However, since the lane dividers on the road are solid until the signs, this potential loophole is preemptively closed.

Depending on the jurisdiction, signs may only apply to the road after them, so you could validly stop just before it.

This no-escape scenario could be done more easily with just "Stop" and "No Stopping Any Time" signs. But by combining 3 signs, the joke is presumably that it was done accidentally, without noticing the contradictions.

The title text adds even more to the dilemma, posting a 45 miles-per-hour maximum speed limit, but also a minimum required speed of 65 MPH. Since 45 is lower than 65,[citation needed] this is quite the perplexing contradiction.

For another of Randall's adventures in road signage (he does live in the Greater Boston area, after all), see 1116: Traffic Lights. For a similar contradiction, see the title text of 2179: NWS Warnings.


Ambox notice.png This transcript is incomplete. Please help editing it! Thanks.
[A two-lane highway stretching out to the horizon, with the lanes separated by a double solid white line in the foreground which becomes a partially solid, partially dotted double white line as it approaches the horizon. To the right of the highway is a pole with three traffic signs.]
[Top sign, featuring a white rectangle on a red circle on a white background:]
[Middle sign is the No U-Turn symbol, a U-turning arrow with the red prohibition circle symbol on a white background.]
[Bottom sign with red text on a white background:]
[Caption below the panel:]
Oh no.

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I was a driver in the Boston area (where Randall lives) for nearly a quarter of a century and this sign combo would not be that unusual to come across. I remember one three way intersection of streets in downtown Boston where all three streets were one-way _out_ of the intersection; there had been a fourth street by which you once could have entered the intersection, but it got closed off by the construction of a new building. There was another intersection in nearby Somerville where as you approached (on a one-way street four lanes wide) you saw three traffic lights spread out on the far side of the intersection, which displayed at one point in the cycle three red lights over three different green arrows, one pointing each way; so the red lights weren't stopping you from doing anything, you were allowed to go in any direction according to the green arrows, so why were there stop lights on? MAP (talk) 04:11, 17 October 2023 (UTC)

Theoretically you can get around this limitation by turning off the road before the sign and doing whatever maneuvers you need to out in the wide open area to the right or left of the road. It's not a U-turn if you're not on the road, and you didn't enter a restricted part of a road either, and didn't stop on the road. After which you calmly make a turn onto the road when traffic is clear. 02:34, 14 October 2023 (UTC)

I'm pretty sure swerving off of a road is also illegal. SteveTheNoob (talk) 04:41, 14 October 2023 (UTC)
You can always just pull over - if a cop asks, just tell him you were lost or tired or had to take a phone call. And then take the opportunity to ask about the bloody sign! Anonymous 07:30, 14 October 2023 (UTC)

So does making a three point turn count as a u-turn? 02:40, 14 October 2023 (UTC) Wouldn't putting it in reverse stop you briefly as you switched from forward acceleration to reverse?

Yes, this is also an example of Rolle's theorem as seen in 2042. SteveTheNoob (talk) 04:56, 14 October 2023 (UTC)

Immelmann! Hammerhead! Half Cuban Eight! Jordan Brown (talk) 03:21, 14 October 2023 (UTC)

After clicking on your comment, I watched the gif on the right before reading the article. I was expecting some advanced driving technique or something. Imagine my surprise! 11:15, 16 October 2023 (UTC)

You could obey the title text if it was 45 miles per hour and 65 meters per hour, respectively. 04:04, 14 October 2023 (UTC)

Perhaps so, but anyone deliberately occupying a travel lane while going 0.06 kph (0.04 mph = 200 feet per hour) in a 45 mph zone would [ahem] rapidly attract attention for other reasons. If it were 65 *kilometers* per hour (40 mph), you'd have a narrow window of legality (I do drive on a road that has a max 45 / min 30 speed limit). 18:15, 15 October 2023 (UTC)

Take notice of the road markings too. At least here in Europe double white lines are not to be crossed. And they go past the point of the sign.--Henke37 (talk) 07:06, 14 October 2023 (UTC)

Aye - doesn't that combination of dashed and solid lines imply that there will be opposing traffic? Ie, the markings on the road expect traffic to enter past the sign, despite what the signs are saying, which adds another layer of absurd (Ignore the pole signs and use the lane on the right, otherwise the lane on the right can never be used?)
Double lines are also "do not cross" in America. And I think in this case it's supposed to be yellow, the dashed-and-solid combo indicates a one-sided passing zone into a lane with on-coming traffic, and double lines in general are only use to separate anti-parallel lanes of traffic, both of which use yellow. "Solid double white lines" do exist, but are only used in very specific cases. Near me, there's a very congested exit, and the solid double whites are used to indicate "no really, you should have switched lanes ages ago, it's too late now!", but since it isn't a Jersey barrier or a line of rods or even a full on median, nobody actually follows the rule. Anonymous 07:30, 14 October 2023 (UTC)
The one way double lines could actually make sense in the case of a one-way street ahead. If you'd look from the other way, the one-way changes into oncoming traffic. So, to prevent accidents, all drivers have to move to the right line (left, from our pov). In Germany, those lines are quite common in front of dangerous bends. Since overtaking is prohibited in curves, drivers can only move back to their intended lane but not into the oncoming lane. 13:51, 3 December 2023 (UTC)
BTW in Europe, yellow lines are reserved for temporary use, and then take precedence over any existing white lines. Makes lots of sense, because there are so many construction sites here. (And the yellow lines are actually just adhesive tape.) -- 08:28, 14 October 2023 (UTC)
Back when elephants had fur, road markings in the USA were white. Starting in the 1950s, road crews throughout the USA began using yellow rather than white paint. From memory, it took about a decade for the transition to be completed, with more rural roads the last to go yellow. 18:18, 14 October 2023 (UTC)
Not in Ireland - standard road markings are yellow. (And, as far as I understand it, Ireland is in Europe.) 15:32, 17 October 2023 (UTC)

Speaking of lines ... in the USA, "Do Not Enter" signs on open roadways usually signal that the road ahead is one-way traffic coming at you. A driver is thereby warned (for example) not to enter the "exit" ramp of a freeway. However, the road striping indicates that passing is permitted for drivers proceeding forward past the sign ... which is nonsensical if the only legal traffic is coming at the viewpoint driver. I am reminded of the ancient comedy routine, "Somebody went to the Army-Navy store, got himself a sign, looked out his living room window, 'Look, Martha, we caught somebody!'" 19:19, 14 October 2023 (UTC)

And I completely forgot why I was posting in the first place: I think there's good reason to create a full "traffic signs" or "road signs" tag, not just "traffic lights". I know there's a page with a very complicated "this is what the road ahead looks like" sign that just says "good luck", and of course there's "Next Five Miles" and "Ahead Stop". Thoughts? Anonymous 07:58, 14 October 2023 (UTC)

I would support that. I wanted to put this comic into a category but I couldn't find an appropriate one. -- 23:11, 14 October 2023 (UTC)
"Click on all the comics that contain traffic lights" 15:34, 17 October 2023 (UTC)

More thoughts: if you must not make a U-turn to the left, you should do it to the right. And then return on the same lane, because of the double line. And finally, the sign itself may be valid and not contradicting itself; it is your fault if you got on this road. ;) -- 08:28, 14 October 2023 (UTC)

In the Netherlands, the message on signs are only valid behind the sign (with the exception of the "precedence way" (voorrangsweg), where outside of built-up areas, the signs are after a junction (though technically... way before the next junction) , so a driver stopping /u-turning here wouldn't be violating anything except the double white lines. Also, stopping out of necessity (e.g. the car in front is also stopped) is never illegal. IIVQ (talk) 09:06, 14 October 2023 (UTC)

Stopping on a road with double white lines to your left may count as obstructing the road, which I can imagine to be illegal in many places? Gpvos (talk) 10:02, 14 October 2023 (UTC)
I believe in the UK the location of the signs doesn't determine the scope of their applicability at all - that's defined by the related traffic order. So it's possible that you might be legally allowed to turn, etc. past where the sign is, but equally you may be committing an offence by doing so before it, and you've no actual way of telling. 15:39, 17 October 2023 (UTC)

If I had to comply with these instructions, I would just put the car into reverse and argue that I was never "stopped". If I actually saw this in real life, I think I'd just slow down, put on my hazard lights, and make a u-turn when appropriate.Jsnider3 (talk) 10:52, 14 October 2023 (UTC

To go from forward movement to rearward movement, you would have to, at some point, even if only for a fraction of a second, to have stopped. 15:41, 17 October 2023 (UTC)

UK equivalents: UK traffic sign 616.svgUK traffic sign 614.svgUK traffic sign 642.svg (Mounted vertically, obviously, and the Clearway would have to be the small version as a repeater/reminder, already being active).
...and Title Text would require suitable numeric alterations on: UK traffic sign 670V20.svgUK traffic sign 672.svg 11:51, 14 October 2023 (UTC)

"Depending on the jurisdiction, signs may only apply to the road after them" - uh, in which jurisdictions is that not the case? How could you adhere to the signage before you see them? -- 15:01, 14 October 2023 (UTC)

I don't know US signage, but there are times over here in my locale when there's repeater/reminder signage, the situation (such as not being allowed to stop) already being in effect past a prior point. Or even "this is information you, as a driver, should already be able to infer from the rules of the road, but some of you are idiots and need A BIG HINT about something that you clearly have forgotten since the time you had to pass your driving test..." erected by the authorities. 19:49, 14 October 2023 (UTC)

Since the lanes are separated by white lines instead of yellow, that means that the two lanes of traffic are going in the same direction. There isn't any roadway visible onto which one could make a U-turn even if it were permitted. -- 23:07, 14 October 2023 (UTC)

That sort of thing varies by jurisdiction. White and yellow are common because they work well and are cheap. -- 07:30, 15 October 2023 (UTC)

Don't minimum speeds require the vehicle to be able to go that fast, but not actually drive this fast at all times? --Coconut Galaxy (talk) 07:42, 15 October 2023 (UTC)

Am I the only one who sees a Gaza Strip evacuation subtext in this? --GregXKCD (talk) 15:33, 15 October 2023 (UTC)

Possibly. There was a similar comment above, but that was also posted by you. -- 20:06, 15 October 2023 (UTC)
ha! thought it failed to post first time, wasn't really trying to belabor the point. -- 21:32, 15 October 2023 (UTC)

This is pretty much the plot of every Irish saga, except with geasa instead of road signs. 17:13, 15 October 2023 (UTC)

Not even that uncommon. I find no U-turn signs get placed places where a lot of people do u-turn, often because they NEED to make a u-turn due to another previous sign issue. So having to do u-turns where no u-turn signs are, is like the f'ing default. 08:41, 16 October 2023 (UTC)

Now, I don't have my driving license, but I'm pretty sure the law of the principle of explosion allows you to ignore all rules in this scenario. 11:26, 16 October 2023 (UTC)

UK traffic sign 622.8.svg No vehicles carrying explosives allowed... 18:15, 16 October 2023 (UTC)
That's no vehicles carrying peacocks. 15:44, 17 October 2023 (UTC)

I can't be the only one that sees a Gaza strip evacuation subttext to this.

out of luck buddy -- 12:46, 29 April 2024 (UTC)

"No stopping at any time" and max/min speed contradiction[edit]

The "No stopping at any time" never applies if it is not possible to continue. If there's a traffic jam, nobody expects you to continue going and hitting a preceding vehicle. I'm pretty sure this meaning is the same in USA as it is in Europe.

In Europe, speed limit takes absolute precedence over minimum speed, and for clarification, minimum speed only means that vehicles that cannot sustain minimum speed are not permitted on the road. It also signifies that if the road is clear and weather permitting, it is safe to drive at that speed. But, if you're not confident in your driving ability, or in inclement weather, or if there is traffic, or for any other reason, you're not expected to continue driving at that speed. Motorways and expressways in Europe have an implied minimum speed of about 60 km/h, but if there are roadworks which have a posted 50 km/h or 40 km/h speed limit, you're not expected to drive 60 km/h and you'll be violating the law if you do.

To Obey the signs you need to "Drive like Xeno", approach the signs at ever decreasing speed without actually come to rest, or passing the no entry sign. 00:52, 17 October 2023 (UTC)

Self-driving test car running overtrained metamodels approaches the signs. Time itself begins to slow down in proportion to nearness. 01:06, 17 October 2023 (UTC)

This is not a problem for flying cars or mole drills. 21:26, 13 November 2023 (UTC)