This question is based on a real world scenario…

There is a causeway, roughly 1/4 of a mile long, over which the tide rapidly rises twice a day, rendering the tourist hot spot at the wrong end of it cut off from the rest of the country for several hours at a time.

Every year there are numerous incidents of cars caught out, in the middle of the causeway, occupants on the roof, awaiting expensive rescue.

There are warning signs, but as we know warning signs are often not heeded and anyway, these signs simply say 'check the times' and barriers would not work as there is plenty of flat sand around the causeway

There is also a problem with people running late, who know the time but can't afford to be stuck for hours waiting for the causeway to become passable again

The question is this:

How can a causeway and its surrounding environment be altered in such a way as to ensure that as few people as possible are caught and left requiring expensive rescue?

  • Is the problem that people don't know the causeway will become unusable, or that they don't take heed to the times? Commented Jul 4, 2013 at 20:05
  • the problem is that they don't know or take heed of the times
    – Toni Leigh
    Commented Jul 4, 2013 at 20:06
  • 2
    install a gate to limit access and hire a human guard to kick people out an hour before the tide? ... or slope it so it can't possibly flood in the middle Commented Jul 5, 2013 at 2:28
  • 9
    Relevant: Refuse to rescue anyone. Let them drown. The rest will soon learn.
    – Kai
    Commented Jul 5, 2013 at 10:19
  • 2
    Who gets stuck? The locals because they think they know better? Or the tourist because they don't know? You might need to address both crowds differently.
    – ptyx
    Commented Feb 10, 2014 at 19:35

12 Answers 12


The cheapest option is a simple sign, but that needs to get the message across.

Flashing lights help as they are a standard "Do not pass" symbol, and they can be turned on automatically. Include a fairly substantial charge for the lifeboat recovery (which is arguably the real deterrent!)

Here's a mockup which might appear in the UK:

enter image description here

  • 3
    A picture of the consequences if you disregard the message goes a long way to making people understand why they should pay heed. Stating the reason why someone is being limited/forbidden/directed increases the chances of them heeding the message. In areas where the "dogs on lead between 15 march and 15 july" has been followed by "because of breeding season" I have seen more people putting there dogs on lead than in areas without that explanation. Commented Jul 5, 2013 at 10:16
  • 1
    A huge fine is a fine idea (pun intended). Deters people from crossing and covers the rescue cost when people /do/ take the gamble.
    – Kai
    Commented Jul 5, 2013 at 10:27
  • 7
    I'm not conviced the fine even needs to be huge. Even a small amount would probably work just as well as a reminder of negative consequences. People getting marooned probably aren't making a gain/loss calculcation and gambling on the odds, they're just not thinking about negative consequences. Commented Jul 10, 2013 at 6:45
  • 2
    @IlariKajaste: I'm not so sure a small fine would be OK. Freakonomics found that, in at least one case, small fines run the risk of causing an increase in poor behavior. You've gone from "forcing the city to waste resources rescuing me is bad" to "the city charges a nominal fee for rescues."
    – Brian
    Commented Oct 28, 2014 at 2:40

Lowering the end-points of the causeway so they get physically blocked first could be an option.

They could be so deep that they are already underwater when the time needed to cross the causeway is longer than the time left the tide requires to flood the whole thing.

  • 11
    This would seem to make the whole thing even more dangerous, you could get on the causeway thinking there is still time, manage to cross past the point where you would otherwise be safe, only to find water preventing you from leaving the causeway.
    – Gala
    Commented Jul 4, 2013 at 22:04
  • 1
    I see two problems with this ... 1. You could very well end up with cars stuck in the lowered end points 2. Depending on the physical attributes of the causeway you coulde have an unacceptable effect on the total amount of passable time per day
    – Toni Leigh
    Commented Jul 4, 2013 at 22:24
  • 1
    Yes you're right. maybe if it's not really deep and still crossable it would signal "shit gets serious soon!" but the people insinde could get out.
    – K..
    Commented Jul 4, 2013 at 22:43

My guess is that with only static signs, people distrust the information and use their own judgment. Which is wrong.

Suggestion: an electronic sign, with a read out like "Safe time remaining to use causeway: 5:32". Or: "Tide rising. DO NOT CROSS. You will be stranded". Since the information is more specific, it seems more trustworthy.


Or even include "16 cars stranded this year. 1000 pounds each."

  • I like this, configured somewhat like @Andrew Leach's answer above.
    – Keith G
    Commented Feb 10, 2014 at 13:55

I know a few such causeways, I think many “easy” solutions are available, starting with turning them into bridges or ferry services. You stipulate that a barrier would not work but I am not so sure. If something that looks like a barrier with a danger sign is closed, would many people drive on sand (itself possibly hazardous for the vehicle) to get around it? If that's the case, you could always cordon off the sand with or add a blinking traffic light or “tide coming” sign to make it look more pressing.

None of this is out of the reach of modern civil engineering, here are some pretty impressive examples). The problem is not so much inventing potential solutions as finding the right cost-benefit trade-off (including building costs of course but also ecological/landscape consequences). I would guess the causeway is still there mostly because it's relatively cheap, adds some cachet to the place and allows the water to flow further inland and protect the tidal ecosystem.

One thing you did not specify is whether the people getting stuck are visitors, locals or both. This little piece of user research could give some cue to the exact nature of the problem and potential solutions (e.g. informing of the danger in general, focusing on enforcing the rule or providing more precise information to support the decision to get on the causeway).

  • in the real world example I mention the people are not local
    – Toni Leigh
    Commented Jul 4, 2013 at 22:23

By the time the tourists are approaching the causeway to return back to the mainland, it'll be difficult to change their behaviour - they have a very strong motivation to ignore the warning signs and try and cross anyway, not wanting to be stuck until the next tide. So a more effective UI might aim at making sure the tourists know the time before they start the drive home. Possibilities:

  • Have a siren within the tourist hotspot, giving a 15-minute warning before the causeway closes.
  • Tell the tourists, as they arrive, what the last departure time will be: enter image description here

For locals who know the tide times but are tempted to risk it anyway, other measures will be needed on the return road.


No one method would work. But a couple of methods, could be. - Text this number and we will send you a text when you should leave. - Fine of 50 (whatevers) for a local charity if we have to save you.


How can a causeway and its surrounding environment be altered in such a way as to ensure that as few people as possible are caught and left requiring expensive rescue?

Raise it to a level above high tide?


Stop rescuing vehicles. The rest will learn. And a few abandoned flooded-out cars would be an effective deterrent.

On a serious note, automatic barriers should work - put up fences (or traffic bollards if pedestrians should still be allowed to enter the area) to the sides of the barriers, for say a couple of yards, to deter people from driving around the barrier.

A detector (IR beam / pressure plate? I have no idea how barriers typically detect vehicles) on the causeway side of the barrier would allow vehicles on the causeway to exit if they're caught in the middle, but not allow vehicles on - unless they employ some Mr Bean-worthy measures.


For a stretch on either side, you can put up temporary barricades. At the same time, plant indigenous bushes or trees along the barricades. When the foliage is sufficient enough to prevent passage, remove the temporary barricade.


If visual cues and even a barrier is not working, I would suggest a slightly higher-tech solution: to use a water level indicator that sets off a really loud alarm when the water levels rise to certain heights(when the causeway should be deserted). A series of red, alarming lights along the railing of the causeway would definitely help convey the message.

Due to these alarming signs, when the unaware visitors' attention is turned to the notion that something could be wrong, easily readable signs describing the danger should be available on site, to answer their doubts.


Lots of great ideas already. Some information that could be added to the signs include:

  • A count of the "number of people who got stuck this year"
  • The cost to the council or whoever pays "£xxxxxx spent rescuing people who ignored the sign"
  • The cost to others for example: while people were being rescued for ignoring signs they emergency services weren't attending more serious incidents

On a lighter note: have a retractable ramp that raise up, so they can jump across Dukes of Hazzard style :)


Lay tire spikes down during the prohibited hours, if they try to go ahead they get stuck BEFORE the causeway. When the causeway is open roll them back up.

During this time a ferry or boat could be available to those who can't afford to wait.

  • you'd just end up rescuing cars from an awkward place with burst tyres instead of from the water, not as tricky, but still awkward !
    – Toni Leigh
    Commented Feb 10, 2014 at 19:53
  • It's not the state's job to tow a car with burst tires. They aren't in danger. That being said I think it's getting increasingly obvious who the americans are (myself included). Commented Feb 10, 2014 at 19:54
  • True (I think, but not absolutely sure), but that car would still need shifting before the tide rose
    – Toni Leigh
    Commented Feb 10, 2014 at 19:55
  • Well the idea is you'd lay the poppers to the entry of the causeway outside of danger of tide, and if that's not possible you'd set jetties to create a chokepoint, which would prevent popped cars from being in range of tide. On a side note how many people die a year from this? Commented Feb 10, 2014 at 19:58
  • As far as I'm aware no one has died, I think the water is only deep enough to leave them stranded on the rooves of their cars, but they still need rescuing !
    – Toni Leigh
    Commented Feb 10, 2014 at 20:15

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