# Automobiles after the apocalypse

So last year I started writing a post-apocalyptic story, and then realized I had no idea what the world was really like, and quite a few things just didn't seem to make sense.

One of the biggest that jumped out at me was the abundance of running automobiles tooling around in my story. Which got me thinking: Could such a thing really happen?

To set the stage, the short version is that in the near future Earth was the target in a cosmic shooting gallery of cataclysmic proportions: While no single blast even matched, say, the Tunguska event, there were so many across a period of many days (weeks, even) that virtually the entire surface of the planet was devastated, and every major city (and many minor ones) was pulverized into oblivion. (What no one in this world (yet) realizes, though, is that this was a targeted attack intended to wipe out civilization, but not necessarily exterminate the planet.) Cue the inevitable collapse of every recognizable society, and fast forward a few years to the scrappy survivors of the human race having banded together into communities of virtually every description scattered across the ruined wasteland of their planet.

Now, certainly, any vehicle that survived this apocalypse, and could handle the terrain of this new world, would be usable for a certain period of time afterward, certainly at least until it ran out of fuel. And no doubt there would be opportunity to scavenge some fuel here and there, but with essentially no more oil rigs, let alone refineries or the infrastructure to distribute these products, certainly fuel wouldn't last long, would it? And of course there's the myriad of other fluids that have to be periodically topped off or even replaced. Maintenance would be another difficulty -- spare parts might be easier to come across, and for much longer, but eventually you'd break down somewhere without access to what you need.

So really, I suppose the question is: Given the utter destruction of modern society, how long could one expect motorized vehicles to continue to be usable by the survivors?

• I don't have the knowledge to calculate a general answer, but I would like to point out that the battery on my vehicle died after two weeks of not using it one summer. Idle battery life is one limit to think about. – Vulcronos Oct 2 '14 at 18:03
• @Vulcronos Good point, though with solar, wind, etc. power it's not impossible to recharge a battery, and if the vehicle's getting at least semi-regular use it should last quite a while (I had a minivan that, when my dad sold it after almost 10 years, was still using its original battery). – Kromey Oct 2 '14 at 18:05
• Yeah. I figure battery life would prevent a car from immediately working but any way to charge the battery could overcome this given time. If you are being chased by the zombie horde, a dead battery could be a death sentance. – Vulcronos Oct 2 '14 at 18:08
• Could you give us some percentages or numbers on how many survivors we're talking about and the amount of land that's not bombarded? I wrote an answer making some assumptions, but while calculations are easy, I'd prefer it to match your setting rather than some arbitrary assumed level of destruction. Since you said there's plenty of cars, I'm wondering how much that is exactly. – mechalynx Oct 2 '14 at 20:31
• The "World War Z" book goes over this exact problem, which I found interesting. – Mooing Duck Oct 3 '14 at 0:39

updated tl;dr: fuel is a problem, so is wear - alternative fuel sources will be required, as will some serious mechanical skills to patch the cars - for a 1st world country that has mostly newer cars, expect most to break down within 2 years, with very few left after 4-6. Calculations below.

Some variables I dug up to help calculations:

all numbers are approximate and correspond to values taken for years 2009-2013 as far as I know. Also, using scientific notation to prevent zero overload. Rounding is performed on an arbitrary basis.

also fuel units are in gallons and barrels because that's the units they're reported in online - I would much prefer metric since I don't live in a country that uses imperial units, but gotta bite the bullet this time.

## Worldwide numbers

usage and production:

• Total number of automobiles: 1e9-1.2e9[1]
• Total number of automobiles produced per year: 80e6-90e6[2]
• Total number of barrels of gasoline produced per year: 8.03e9[3]

Now we need to check distribution of these across people and cars. I'm electing to use US numbers here since they're more readily available and the US seems to have both lots of cars and consume lots of gasoline, so if the numbers work out for the US, they should work in an apocalypse - if not, we can adjust them downwards to see how far we'd have to go until it's workable.

## US numbers

usage:

• Total number of automobiles: 250e6[1]
• Automobiles per capita: 800 per 1000[4]
• Total gasoline usage in barrels per year: 3.2e9[5]
• per day: 8.77e6[5]
• per automobile per day: 0.03508

production:

• Total number of automobiles per year: 11e6[2]
• per day: 31e3
• Total number of barrels of gasoline per year: 3.4e6[6]
• per day: 9.6e3

Now, I know nothing about average compatibility of parts between automobiles. It might be high or low, or anything in between, so I'm not going to include it now. There are obviously other factors that influence maintenance and usage: battery lifetime and wear, makeshift solutions, alternatives used, dangers and vast numbers of cars destroyed. I'm going to assume none of these factors play a role for now.

What I am going to assume is that the world goes to hell pretty quickly - in a matter of days. Lets be generous and say that despite the bombardment, we get 2 days worth of production done before production stops abruptly. Lets also assume, all cars in the world have half their tank full and assume that this means they have about 8 gallons in there[7]. Since major cities are completely obliterated, we have to find out what percentage of people and cars are left. Lets say 20% of people and cars are outside city centers[8][9]. Of that 20%, we'll assume 5% survives the bombardment, since most of the surface is destroyed. That leaves:

• Automobiles: 1.25e6
• Survivors: 3.6e6

• Gasoline barrels left in cars total (42 gallons per): 240e3

• Gasoline barrels produced but unused before apocalypse: 19.2e3
• total: 260e3

edit - I originally had calculated that fuel availability would last an outrageous 20 thousand years, which is horribly wrong. Brian Drummond in the comments caught the error and with the proper calculations (aka, calculating for all cars not just one) it turns out that with the amount of cars left and the daily consumption of fuel for a city car today (which is about 10 miles per day), there's about 6 days of fuel left (again, lol).

This scarcity is further compounded by my original estimate of how far cars would travel daily, which I placed in the range of 60-125 miles, since the daily consumption was equal to about 10 miles, which is too low for a post-apocalyptic world (you want to save fuel so you either don't use a car or use it to travel long distances). If we assume about 100 miles average use whenever you move a car, we're left with about about 15 hours of continuous driving (this assumes the tank has enough fuel for ~150 miles plus its share of fuel from what has been produce in 2 days within the country[7]). That means, if every one of those cars where to travel on the first day, trying to escape or find safety, they'd be out within the day. There'd be no usable fuel left, not even in refineries, gas stations etc. - so the calculations about how long it would take for cars to break down must assume an alternative source of fuel, which of course, if not ideal for the car's engine, will cause it to fail sooner. Cut the amount of cars to a fourth per year! Unless you have statistics on how many older cars exist - if there's lots of them, you might have more cars left. See vsz's comment for more details.

Also, as the numbers stand, we have 3.8 (lets say 4) people per car which leaves no room to say "yeah but what if less cars are used?". Even if less cars where used, we're obviously in the range of days rather than hours - not a big improvement. If you add the weight of equipment and provisions to the estimate, it's even more bleak.

If you want to see the original text, just see the edit history

Now how long can we expect a car to work until it breaks down? Lets assume cars last for 100e3 miles on average (half of what they're expected to if maintenance is available[11]) and they're already half-way there, so about 50e3 miles left on each car on average. Based on the average daily consumption of gasoline and the average fuel efficiency[7] we get about 10 miles per day which is very low, so lets assume a highest bound of 125 miles per day. That gives us about 400 days average life for each car, a bit over a year. If the average usage is half that much, we get 800 days, which is a bit over 2 years.

Obviously, people skilled with car maintenance, with available parts or scrap to turn into parts and a bit of creativity will get them working for longer, but I doubt you'll get cars older than 5-6 years still in working condition. Of course, that's speculation.

So I'd say, as a rule of thumb, halve the amount of working cars every 2 years after the apocalypse. After a decade, you're left with about 40e3 cars in the US, most of them hosts to parts of their fallen brethren. In 20 years, you have about a thousand cars left. This further removes fuel as an issue - it will never run out by car usage alone, but the cars will run out pretty soon.

• This is brilliant, exactly the type of answer I was looking for! I can massage these numbers to fit precisely the impacts of my particular apocalypse (for e.g. the hits were focused on population centers, so we could expect a higher percentage of rural dwellers to have survived), but it's more than enough to fix this up and even toss in a few lines of dialog to explain them to the reader! Thanks! :) – Kromey Oct 2 '14 at 20:49
• Excellent answer, I wish I had votes left :). You should also consider that older cars are more likely to be kept running. Newer ones have computers, specialized gear, etc. – Tim B Oct 2 '14 at 21:17
• @ivy_lynx : Yes, as someone who grew up in Eastern Europe I can attest that car generation makes a big difference. Up until a decade or so ago, most people used 20+ or 30+ year old cars. They were loud and uncomfortable compared to modern cars, lacked a lot of features most people take now for granted, but they were so simple that an average car owner could repair them by themselves. Older cars could run on fuel with much lower quality, which would be a big advantage in a post-apocalyptic scenario. Fuel and tires would have to be improvised, so their quality would be very poor. – vsz Oct 4 '14 at 16:01
• Your fuel estimate of 20000 years appears to assume that all the fuel available (7.4e6 days) is for one car. It's actually 7.4e6 car-days worth of fuel. Or for 1.25e6 cars, about 6 days worth - assuming everyone shares nicely! – Brian Drummond Oct 5 '14 at 19:44
• @Kromey made the changes - but ignore my previous statement about reducing people to .5% giving us years of fuel - I shouldn't try to think without sleep - it's another blunder. I'll make a pass over all this at some point just to make sure, but it should be ballpark accurate I think. – mechalynx Oct 6 '14 at 0:48

Something I haven't seen mentioned yet is that modern gasoline blends actually have a pretty short shelf life. Unless your post-apocalyptic survivors have taken special precautions, most of their gasoline reserves will be unusable in just a few months. I would expect this to be a problem long before any of the other parts start wearing out. Older-model, bio-diesel-powered vehicles seem a lot more plausible though.

References:

or just google "shelf life of gasoline"

In addition to batteries and fuel, I'd worry about tires. The unerring interwebs talk about six years as the manufacturers' recommended shelf life; most would probably still be acceptable for several more years, in a post-apocalyptic setting, but prone to sudden blowouts. Handy when you need a plot device!

The slow decay of tires is affected by low-atmosphere ozone levels, which should drop quickly if industrial civilization stops. However, asteroid impacts would damage the high-altitude ozone layer (), increasing UV levels at the surface, and therefore accelerating the decay of tires in the open. Scavenging tires from cars on the side of the road will therefore probably be futile after a few years, but tires in buildings, especially if wrapped or otherwise protected from air, may be good for much longer. Very valuable!

You may want to ask another question, "can one improvise car tires?" FWIW, Mythbusters did OK with solid wood.

• Fascinating, I wouldn't have thought asteroids impacting the planet would significantly affect the ozone layer. I'm not too worried about tires, though, you'd be able to pretty easily walk into a ruined Wal-Mart and pick out a new set any time you needed. Good point on them being prone to blowouts, that may have to feature in my story -- if the cars survive at all, that is! – Kromey Oct 2 '14 at 20:42

I believe that early tractor engines were designed to run on vegetable oil because that is what would be available to farmers out in the far reaches. They could be self sufficient for their fuel. We still have bio-diesel engines and you still hear about the conversions to use McDonalds used frying oil. So would automobiles be around, certainly plausible. Would they run on gasoline? Not real likely, though if humanity is wiped out in large swaths then it could take a long time to use up what can be found in station tanks. Decent roads to drive them one could be a bigger problem

• Regarding the point about old tractors, hot bulb engines is one kind of engine that can run on almost anything that you can make burn. However they are pretty rare these days. – a CVn Oct 2 '14 at 18:20
• Hadn't thought about biofuels, though thinking about it now there's even ways today to convert gasoline engines to run on them. But don't those pretty much rely upon the scale of McDonald's serving umpteen million burgers? Would they be even remotely feasible in the smaller scales of civilization being knocked back to Medieval European scale? – Kromey Oct 2 '14 at 18:25
• Well with fewer people you will have a much smaller need and people will be more likely to think about their travels more than just take off and expect to have a fuel source when they run low. – bowlturner Oct 2 '14 at 18:35
• Any Diesel engine not just tractors will work on vegetable oil (that's what bio fuel is) there are certain additives that make it better for the engine and cold temperatures might cause problems, but that's all diesel is, is another kind of oil. – Toby Allen Oct 2 '14 at 19:54
• @bowlturner But then again while there may be fewer people, repeated asteroid hits would have done quite a number on existing fuel stores... – Kromey Oct 2 '14 at 20:44

Going through this very same topic. Blended petrol have a lifespan of about 3 months. diesels maybe 6 months. There is one company doing stabilisers and refreshers but you need to keep adding them every 3 months or so. Fuel left stood turns into shellac, even in sealed containers. Its fine for heating but not running an engine on. Vegetable oil might by an option, it needs lye and methanol, which aren't tricky to make. A drawback might be the shelf life of vegetable oil, I'd have to check on that. Fuel ins't an issue, there are plenty of Compressed Natural Gas vehicles about. As long as the containers are fine and don't corrode it doesn't really have a shelf life. There is plenty of natural gas around so its easy to obtain, and a biodigester, like Mad Max Beyond Thunderdome is feasible. Growing a biodiesel crop isn't really an option, it takes a lot of acreage to make fuel, and you need to be growing food. Batteries are an issue, modern rechargeable are ok for maybe 5 years. Lithium watch batteries are the best at 15 years, but so small. Old lead acid batteries are probably the most viable solution; they can be rebuilt. Solar panels generally have a viable lifespan of 10-15 years, their yield degrades rapidly. Wind turbines need a lot of maintenance, due to being so exposed to the elements. Steam, from gas, coal, biomass boilers, is a much better option. Plenty of small steam turbines in factories and they can run a few megawatts, Also worth looking at diesel electric trains, they use a diesel engine to drive a turbine to generate electric for the wheel motors. Tyres are the clincher. Current recommended life span for tires is 6 years, from date of manufacture, that's stamped on the tyre. They oxidise so maybe vacuum packed, but I would think no more than double that. I'm looking into urethane and synthetic tyres, but a lot use petroleum products and its how much crude oil is left, and can you refine it.

There have been quite a few settings that revolved around this concept. Some...much better than others.

The first that comes to mind is Road Warrior, ah, Mel Gibson before he was totally crazy.

I think you have a couple options or rather a time range of options. For the first few months to years (depending on depopulation levels, more depopulation the longer the gas lasts) you should be fine with cars being fairly common.

The second phase would be a gradual reduction in the number of cars to the point where you hit

Stage 3. Essentially there are no running vehicles left, and to add a little flavor I would just like to say that I have seen a 4 door sedan being pulled by a pair of donkey's before...that pretty much describes stage three.

So if the inclusion of vehicles is important to you, have it happen sooner after the cataclysm, less cars, have it further down the road...metaphorically speaking.

• Yeah, looking back over some of my scenes, there were definite Mad Max influences present... – Kromey Oct 2 '14 at 20:40

One option for fuel that doid not come up yet is wood gas. This has been done in France and Germany during WWII, when fuel was not given to cilivialns easily: BAsicall you build a sort of oven that burns wood with not enough air for complete combustion, the resultin gas is combustible and can drive your motor. Wood gas vehicles need frequent fuel stops (wood is far less energy-dense per weight or volume than gas), mor maintenance and have less power but it can be done.

Look around the internet for pictures and tips on how to convert cars so you know how your cars will look like. One starting point couild be here.

• That's an interesting idea, possibly easier to take advantage of while on the road than biofuels... – Kromey Oct 5 '14 at 23:41

While other answers have pointed out various limits that are realistic I thought I'd point out there's a "loophole" if you will for each of them.

• The autos would have part wear for sure but regular disassembly and cleaning plus lubrication can drag it out for a very long time. Driving cars at slower speeds reduces wear and resource consumption tons.

• Oil can have an indefinite shelf life.

• Gasoline can last 25+ years in a metal can with some stabilizers. (if you can find gasoline you can probably find additives).
• If there's enough meteors to wipe out each major city then your looking at a huge drop in population so there are extra cars lying around everywhere for spare parts. As far as massive usage of cars in the midst of the attack... Let's be honest if there's meteors filling the sky is your first thought going to be "To the bat-mobile!"? No, its going to be "To the bomb shelter!".
• Diesel engines can run on vegetable oil with minor modifications. As far as I'm aware you could generate electricity and grow corn to produce corn oil pretty easily.
• Batteries even if continuously recharged and unused lose a certain percent of life. However you could convert back to a hand crank design pretty easily.
• The tires point is a good one but they also provide the solution: wood (thanks for that).

So to summarize if you had a decent enough repair man and a source of electricity to make oil (abandoned plant, wood powered steam engine, hand cranked alternator) you could keep a car running for a pretty long time in such a scenario and if you got a hold of certain parts probably pretty close to indefinitely. (I'm thinking zero wear plastics, ceramics, or super-alloys like you might find in racing or experimental parts but used at <40 mph on a regular car).

It however would definitely be hard as you would need to find the solution to each issue rather quickly to prevent the issues from being "insurmountable". If nobody paid attention to the issues it would be pretty easy, as others noted in their answers, to run all the viable autos into the ground.

• "Oil can have an indefinite shelf life." Need a source for this. Because scientists say otherwise. – Carlos2W Nov 18 '16 at 21:41
• @Carlos2W I'm not going to source my rebuttal as it's mostly just a general feel thing from researching. But as far as natural oil from crude, it seems it does have an indefinite life, the additives which are an important factor for the engine gel out of the oil and/or separate. But for an apocalyptic scenario getting the job done (just not as well) vs not getting it done is pretty obvious. – Black Nov 19 '16 at 4:39

Ok, first of all gasoline has a short shelf life. In just a few months it will go bad. Even if you use fuel stabilizer and keep it in an air tight tank it will go bad after two years. There is also avgas, but avgas only has a shelf life of a year in ideal conditions. Diesel has a shelf life of a year as well. To me, the car that would work the best is an electric car but recharging a car in an apocalyptic world would be hard to do. Or you could look at some of the older cars that run on propane. It has an indefinite shelf life depending on the shape of the tank, propane does not go bad if it remains sealed.

• Is the shelf life of two years longer or shorter than how quickly it would/could be used up? – Mithrandir24601 Oct 27 '17 at 20:53