# Truck through the Tunnel [closed]

This might seem familiar to many of the veterans here, but since it has not been exclusively asked, I am posting it.

A 13-foot tall truck is at the entrance of a tunnel with a clearance of 12 feet 11 inches.

What is the most economic and simplest solution possible that the driver of the truck has at hand to pass through the tunnel safely to arrive the other side with the truck?

N.B. As the problem implies there are multiple solutions possible. I am expecting a specific answer which on consensus of the reader(s) can be regarded as the acceptable answer.

Disclaimer: I did not create this puzzle but heard it way back in the 80's as a young kid. I think it is a Edward De Bono puzzle.

Anyways the alternate answers are rarely documented which is what I am after. Investing further time to curate through the list of answers is no longer possible and am accepting the classical answer.

• Having watched far too much Looney Tunes as a child, I suggest the following: 1) paint the wall above the tunnel to look like the interior of the tunnel, giving an (illusory) extra foot or so. 2) find a coyote and induce it to chase you. 3) Drive through the now 14' tall tunnel. 4) (optional) laugh as the coyote runs into a painted wall 5) meep meep Aug 3, 2015 at 15:50
• My first instinct is to say "it cannot possibly do so" because my default picture of a tunnel is circular (or at least, say, the upper four-fifths of a circle)... if it's 13' high at the center, a 13' truck would never get through. Aug 3, 2015 at 15:56
• A version of this puzzle - complete with Bailey M's answer - was included in the film "Working Girl" (1988). Might this have been where you originally heard it?
– user9278
Aug 3, 2015 at 16:04
• Would it be possible for you to edit this question to limit the scope of possible solutions? This could potentially be done by more specifically defining what you mean by economical/simplest, or by limiting the possible scope of out-of-the-box answers.
– user20
Aug 3, 2015 at 17:54
• Get a great number of migrants to get inside the truck and weigh it down. This would work very well at the moment with the Channel Tunnel. dailymail.co.uk/news/article-3183668/… Aug 3, 2015 at 19:58

My first instinct would be to

Let some air out of the tires, so that you end up riding an inch or so lower and can pass through safely, albeit maybe a bit bumpy.

• Excellent !!!!!. Aug 3, 2015 at 15:22
• This is, in fact, the classical answer to this riddle. Aug 3, 2015 at 16:34

Assuming the measurements are completely accurate, then a solution is:

To drive the truck through the tunnel! For peace of mind you might want to grease the roof. As long as the tunnel is uniform, and straight, and the truck doesn't move in such a way as to ever increase its height, then a 13' object should fit through a 13' gap.

• +1 This was actually my first thought. I had to read through the comments before I figured out what the problem was supposed to be. Aug 3, 2015 at 17:57
• I've edited the problem to make it more in line with the versions of the problem I've heard, which make it less ambiguous by using terms like "clearance".
– user88
Aug 4, 2015 at 5:51
• @JoeZ. Fair enough, I think that must have been a difference between this and other versions of the question :) Aug 4, 2015 at 7:55

Many large trucks have:

Adjustable air bag suspensions which can be lowered. Simply lower the ride height and drive right through.

Blast the A.C. so the truck shrinks a few mm.

• Please add an explanation of how blasting the air conditioner would shrink the truck, or this answer might be deleted.
– JLee
Aug 3, 2015 at 16:25
• @JLee things get smaller when they're colder. en.wikipedia.org/wiki/Thermal_expansion Aug 3, 2015 at 16:34
• an air conditioner removes heat, so, part of it is giving off heat equal to the amount of cold it is giving off, so there is no net change. but even more importantly, would changing the temperature inside a metal framed truck by 10 or 20 or even 30 degrees really be enough to affect the size of the truck?
– JLee
Aug 3, 2015 at 16:39
• suppose the temperature is 18 C, or 64 F. Then it would shrink by about: ∆L = α∆TL = 12e-6 x 18 x 390 cm = 0.0846 mm Aug 3, 2015 at 16:51
• @nietsnegttiw It would be expensive. Aug 3, 2015 at 19:44

Since we know that tunnels are mostly shaped like a circular tube, a 13-foot truck cannot pass from a tunnel that is 13-foot or lower. This can be further calculated, by estimating width of the truck, regular tunnel shape and so on.

An economical approach can be changing suspension height, just like people who do lower their cars. If that is not enough, rims can be changed and tire pressure can be decreased.

Although 13 foot is not that high. Most small trucks are lower at size. Best thing to do would be putting the load sideways with some help from cranes. It would not be perfectly stable, but it will do the job.