The year is 203X, and a small-ish asteroid is detected just 24 hours before it hits the atmosphere above central Florida. The kinetic energy is estimated to be "a few" exajoules (1 exajoule being 5 times the energy of the Tsar Bomba if it explodes in the air, 1.4 EJ being a magnitude 9 earthquake if it all ends up in the ground, and nobody's quite sure which will happen). Someone tried to nuke the asteroid, but that just means the asteroid is now radioactive, not that it's been stopped.

On the plus side, Florida has a lot of experience with mass evacuations from all the hurricanes — if anywhere can get its people to safety, Florida can.

How many people can be evacuated from Florida in 24 hours?

Assume near-future tech: self-driving cars are really self-driving (and all electric), but they're still only 1/4 of all cars in the USA, and they're still limited to the sorts of range (and battery charging times) you'd see in a 2022 Tesla. No significant changes to aircraft or shipping capacity. Cunning plans encouraged, provided they can be implemented such a tight schedule.

Assume the Caribbean islands, including Cuba, are happy to assist with ships for the immediate evacuation.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Jun 13, 2022 at 16:47
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    $\begingroup$ @Arvex 1-km sized near-earth asteroids are still being detected each year, so there are probably many 150 meter sized near earth asteroids out there. If they came from the sunward hemisphere chances would probably be good they would not be detected early because telescopes can't look in that direction very well. The closer to the sun's direction, the less chance of being spotted at all. $\endgroup$
    – JanKanis
    Jun 13, 2022 at 22:09
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    $\begingroup$ It depends entirely on (a) there being a plan in place that has been thoroughly tested, (b) everyone being familiar with the plan and willing to do exactly what they are told, and (c) the resources needed by the plan (for example, buses) being available at the time the plan is activated. All rather implausible assumptions. $\endgroup$ Jun 13, 2022 at 22:16
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    $\begingroup$ As a Florida resident familiar with evacuation procedures, I'm confident saying that if our population of roughly 21 million was given 24 hours' notice to leave, the ensuing traffic bottleneck nightmare would allow enough time for about a dozen people to run to Georgia at the last second. $\endgroup$
    – Dan
    Jun 13, 2022 at 22:58
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    $\begingroup$ You may want to read about what happened when Hurricane Rita threatened Houston in 2005. This was shortly after Katrina in NOLA, and folks were seriously psyched out. One of the results was that I-45 can now be switched to all lanes northbound to assist in evacuations. One of the big problems is that most people will want to evacuate by car, and the gas stations will quickly run dry (and there's too much traffic to refill them). hro.house.texas.gov/interim/int79-2.pdf $\endgroup$
    – Flydog57
    Jun 14, 2022 at 22:53

7 Answers 7


In college, I simulated the evacuation of coastal South Carolina as a project for my "Mathmatical Modeling" class. Some ballpark estimates based on the outcomes from that simulation:

  • Assuming orderly evacuation efforts, Jacksonville will be fine. It's not far from the Georgia border, and between them, I-95, US-17, and US-23 provide six lanes of northbound flow -- twelve, if you temporarily reverse the southbound lanes. That's two million or so safe.
  • Tallahassee has a better lane-to-population ratio and a similarly short distance. Expect complete evacuation within twelve hours, giving you another quarter-million or so.
  • Pensacola is probably outside the blast radius, and is right on the border, with plenty of options for travel. Another half-million saved.
  • Gainesville is a bit tricky: you're trying to funnel a half-million people through the four/eight lanes of I-75 and US-301, and the US-301 traffic is trying to get out of Florida on the same roads as the Jacksonville crowd. Still might be doable, particularly if you time the leading edge of the US-301 evacuation to meet the trailing edge of the Jacksonville evacuation.

Three and a half million or so safe. And that's the end of the good news.

  • Orlando has two and a half million people and no dedicated evacuation routes. I-95 (three lanes, six if reversed) and US-17 (one/two lanes) run into the Jacksonville evacuation, while I-75 (two/four lanes) runs into the Gainesville evacuation. Expect some survivors, but not many.
  • Tampa-St. Petersburg (three million people) is also trying to funnel onto the same two/four lanes of I-75 as Orlando and Gainesville; US-19 relieves things slightly by providing a dedicated two/four lanes. Maybe a half-million survivors, mostly from the US-19 route.
  • Miami-Palm Beach is toast. The Everglades provide a severe bottleneck to any evacuation, and even once you get past that, you run into the traffic from every other evacuation. Expect maybe a couple hundred thousand survivors, mostly people who could find or commandeer a boat and make it to Cuba or the Bahamas.

Evacuation by any means other than road can't save very many. The infrastructure for loading millions of people onto boats, trains, or airplanes just isn't there -- you might be able to pack 20,000 people onto the Queen Elizabeth II, but it'll take most of a day just to get them on.

Florida handles hurricanes by moving people away from the coastline. Storm surges extend, at worst, a couple miles inland, and there are plenty of short-distance east-west routes to evacuate people on. Evacuating the entire state using the limited number of north-south routes is a very different prospect.


For fun, let's calculate a Fermi estimate

The easy way to approach the problem is to concentrate on how many people can be moved across the state boundary.

How many roads are there out of Florida? As an ignorant provincial European, I know of I-75. It's a six lane freeway; of course, all six lanes will be dedicated to the exodus. Let's say that all the drivers are excellent drivers, and each lane can carry one car per second. Let's also assume that each car carries 5 people.

6 lanes × 1 car/second × 5 people/car = 30 people/second

30 people per second means 108,000 people / hour. Round it to 100,000 people per hour. In 24 hours, the I-75, under the best possible conditions, can transfer 2,400,000 people out of Florida.

Maybe there is another high-capacity road out of Florida. Maybe I-10? As far as I know, I-10 has only four lanes at the boundary between Florida and À la Bamma, so under the same ideal conditions it can move 1,600,000 people out of Florida per day.

@GrandmasterB indicates that there is also I-95; that's also a six-lane freeway, so we can add another 2,400,000 people.

That's a total of 6,400,000 people exiting Florida in a day. And this is in ideal conditions, with no traffic jams and all cars having some sort of automatic distance-keeping software enabling them to follow one another at one second interval.

Sorry for the other 15,000,000.

(Note that airplanes and ships don't count. They cannot move any significant number of people in a day. The only other reasonable means of moving people out would be by rail, but, as far as I know, the railway network in Florida is rather poorly developed.)

  • 2
    $\begingroup$ @Mindwin: Population density is 156 inhabitants per square kilometer within 30 miles of the northern bounday of Florida? I did not expect that at all. $\endgroup$
    – AlexP
    Jun 13, 2022 at 17:44
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    $\begingroup$ @Mindwin: You assume all the people capable of hiking out will selflessly choose to do so. I guarantee >95% of them would be the ones taking up most of the road capacity. $\endgroup$ Jun 14, 2022 at 10:42
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    $\begingroup$ Why wouldn't ships and planes not be able to carry a lot of passengers? About 350000 people are handled in Floridas Airports each day anyway. I'd assume that those numbers could be doubled in case of emergency. For Ships I'd suspect that container ships could be loaded with a shit ton of people for a day. It does not have to be glorious at all. If one can get 10 people into a container the biggest ships could transport 240.000 people. Remember this has to be only for a day. It will be awful but people would survive. $\endgroup$
    – SirHawrk
    Jun 14, 2022 at 14:00
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    $\begingroup$ @SirHawrk but how many ships are sitting empty in Florida ports? There's no time to empty them after all. Then how far away do they have to get for safety, travelling at ~20mph with a potential tsunami on the way? $\endgroup$
    – Chris H
    Jun 14, 2022 at 14:09
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    $\begingroup$ @SirHawrk: "I'd assume that those numbers could be doubled in case of emergency." You might be surprised by how efficiently airport scheduling is handled nowadays. Most major airports run at close to capacity any time that's not the dead of night (it's why small delays can balloon; miss your takeoff window, gotta wait). You wouldn't need to unload baggage from incoming planes, but they still need to land/take off, and you still need to refuel them and load passengers. I doubt you could get even a 50% increase in capacity out of emergency evacs without planning for it significantly in advance. $\endgroup$ Jun 14, 2022 at 20:20

Not many

If 24 hours is all we have from the first confirmation of asteroid strike, even in the best case scenario authorities won't be able to create effective evacuation mechanisms in time. 2-3 millions, mostly from Northern Florida would be able to make it across the state line. The rest would be bogged down in traffic jams all over the place. Planes and boats can take some people away, but this number will only be in tens of thousands (in excess of what they normally carry off every day).

This is a pity, because potential for quick evacuation is much higher. Cars, buses and trains can take virtually everyone out to safety - if they work in concert. This type of work must be carefully organized - for example, one bus convoy can take a thousand people away at a time moving on an opposite side of a highway - but this is not something that happens every day or even every year.

If authorities are somehow prepared and everyone knows what to do, then most of Florida can be evacuated within 24 hours.

P.S. Just to substantiate my point - Florida has about 60,000 school buses, and apparently at least that many school bus drivers. If we jam pack those buses, millions of people can be moved, but doing this all within 24 hours would be an enormous task.

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    $\begingroup$ So what you are saying is we need Disney to be in charge of our evac plans in order for it to have a chance of saving S. Florida. As one of those residents of N Florida that could make it (93 miles to Ga, all along country back roads if I want/need to), this kinda gives me a giggle... $\endgroup$
    – ivanivan
    Jun 13, 2022 at 16:59
  • $\begingroup$ Florida routinely evacuates large numbers of people. Authorities are quite prepared to reverse the South-bound lanes of I-75 and I-95 to get people out as quickly as possible. If everyone were about to die, I'm sure they could convince the bus drivers to report to work pretty quickly, too. Also, tens of thousands for airplanes + cruise ships is at least 2 orders of magnitude low, perhaps 3. The cruise ships might not be able to get everyone to safety before the tsunamis, though. Even on a completely normal day, hundreds of thousands of people leave Florida by air. $\endgroup$
    – reirab
    Jun 13, 2022 at 19:09
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    $\begingroup$ @reirab I was not fully clear about my "tens of thousands" claim. What I meant is that extra potential would be only in tens of thousands, because airports are already busy as they are. We are not going to bring additional 100,000+ victims to Florida on that day, and that should help somewhat. $\endgroup$
    – Alexander
    Jun 13, 2022 at 19:35
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    $\begingroup$ @Alexander The biggest confounding factor on increasing capacity, especially for an emergency like this where a whole state was about to get blown up, would just be getting people to the airport. The seat capacity could easily hit a million or more in an emergency if they could get the people to the airports fast enough. Things like security screening, baggage checking, and ticket checking could be completely bypassed. The runways themselves aren't all that busy. Plus, they wouldn't have to limit to the huge, busy airports. Lots of smaller ones could handle hundreds of 737s if necessary. $\endgroup$
    – reirab
    Jun 13, 2022 at 19:44
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    $\begingroup$ The parts of the airports that tend to hit capacity are things like gates, security screening, baggage checking, printing boarding passes, etc. All of that could be completely bypassed. MCO alone could probably get a million people out if they could get them to the airport. In an emergency like that, even the requirement for everyone to have a seat could be waived by the FAA, allowing perhaps another 10-20% pax/aircraft. They don't need enough fuel to get to LA. ATL or CLT would do, but you could also add HSV, CHA, BNA, TYS, etc. Then add in the C-130s and C-17s. $\endgroup$
    – reirab
    Jun 13, 2022 at 19:56

24 hours? Panic, confusion, traffic jams ...

First, somebody has to convince the state and federal governments that this is real, and not a rounding error, and not going to hit Tunguska instead. They won't go public unless NASA or the Space Force or preferrably both confirm it.

Next, there needs to be an alert. Fortunately there are Wireless Emergency Alerts. Let's assume that most people receive and believe it. (Some won't get it, some won't believe it.)

Forget ships and cunning plans. You won't get ships to ports and people to ports in time.

Florida has about 22 million people. There are about 8 million cars. So in theory, there should be enough seats in the cars for everybody. In practice, not all cars will travel at full capacity.

Miami to Jacksonville are 350 miles. Even if cars constantly drive 55 mph, that's six and a half hours. But you can expect a traffic jam, instead. A large number of cars will have to fill up, but gas stations cannot cope. Humans being humans, they will get into their cars and try to get as far as they can. Damaged cars or those with dry tanks will clog the highways.

The endurance of a Tesla is marginally enough for the trip, but that's assuming good driving conditions, not this chaos. So discount all electric cars as being unsuitable. Unless there is a special lane on the highway for electric car convoys under computer control, and the social norm of not using that lane with an old gas-guzzler holds up under stress. (Imagine a group of smart cars, all talking to each other and the smart road, cruising along at their calculated cruise speed -- and then a stereotypical redneck with a non-networked pickup full of semi-auto rifles cuts into their lane.)

To make the evacuation with ordinary cars work as well as possible, you need a smart system to match cars, gasoline, roads, and people. Each car is filled to capacity, and only then it gets gas and road space. Impossible to set that up in the remaining time, but perhaps there have been environmental regulations to require (and monitor) car-pooling by commuters? If "just about everybody" has an account, their system might be able to scale up enough.

  • $\begingroup$ I'd say that "in the future" a Tesla (and similar) would presumably have longer ranges considering new tech on the horizon - pocket-lint.com/gadgets/news/… - from longer lasting, lighter, over the air charging. I'd assume the same speeds but self driving cars, with better batteries, better tech? "to make the evacuation work with ordinary cars" needs to be updated for "ordinary" in the future. $\endgroup$
    – WernerCD
    Jun 13, 2022 at 2:15
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    $\begingroup$ Because of drafting, computer controlled cars with minimal spacing would get considerably better mileage than typical conditions. You have to rotate the lead vehicle out since it has the additional burden, but with full computer control even this complicated maneuver would be possible. Creating additional lanes of traffic via narrow spacing between lanes would also be possible.. $\endgroup$ Jun 13, 2022 at 2:34
  • $\begingroup$ 8 million cars, even if in a row bumper to bumper, would reach around the diameter of the entire Earth. There is no way for the vast majority of the cars to even leave the city they started from, if all of them went out the same time in the same direction. $\endgroup$
    – vsz
    Jun 13, 2022 at 4:33
  • $\begingroup$ If the future is any good then they will have the best way of evacuating large numbers of people in record time, good public transport. Trains and buses can move more people than cars. Since it's Florida, ferries would also work. $\endgroup$
    – Turksarama
    Jun 13, 2022 at 5:36
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    $\begingroup$ @WernerCD It's more likely that range will be lower in most future EVs. Once you have good charging infrastructure, lugging the excessive weight of the batteries for longer range is a bad trade-off. $\endgroup$ Jun 13, 2022 at 10:44

Frame Challenge

You don't supply every bit of information needed to complete the analysis, but it's close enough to say that you overestimate the effect of such an impact.

You supply a volume of 1.887e6 m^3, this means a diameter of 153.317 m. And a density of 2450 kg/m^3

You don't specify the angle of impact, so I'll assume worst case of 90 degrees.

Plugging these into the Purdue / University College of London Impact Simulator yields the following result at a distance of 50 km from the impact site.

Crater Dimensions: What does this mean?

Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.

Transient Crater Diameter: 2.57 km ( = 1.59 miles ) Transient Crater Depth: 907 meters ( = 2980 feet )

Final Crater Diameter: 2.92 km ( = 1.81 miles ) Final Crater Depth: 408 meters ( = 1340 feet ) The crater formed is a simple crater

The floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 0 microns ( = 0 thousandths of an inch ). The volume of the target melted or vaporized is 0.0059 km3 = 0.00141 miles3 Roughly half the melt remains in the crater Thermal Radiation: What does this mean?

Time for maximum radiation: 103 milliseconds after impact

Visible fireball radius: 1.55 km ( = 0.961 miles ) The fireball appears 7.03 times larger than the sun Thermal Exposure: 1.08 x 105 Joules/m2 Duration of Irradiation: 22.7 seconds Radiant flux (relative to the sun): 4.79

Seismic Effects: What does this mean?

The major seismic shaking will arrive approximately 10 seconds after impact. Richter Scale Magnitude: 6.1 Mercalli Scale Intensity at a distance of 50 km:

VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.

Ejecta: What does this mean?

The ejecta will arrive approximately 1.69 minutes after the impact. At your position there is a fine dusting of ejecta with occasional larger fragments Average Ejecta Thickness: 3.1 mm ( = 1.22 tenths of an inch ) Mean Fragment Diameter: 11.1 cm ( = 4.39 inches )

Air Blast: What does this mean?

The air blast will arrive approximately 2.53 minutes after impact. Peak Overpressure: 9790 Pa = 0.0979 bars = 1.39 psi Max wind velocity: 22.2 m/s = 49.6 mph Sound Intensity: 80 dB (Loud as heavy traffic) Damage Description:

Glass windows will shatter.

Assuming that the impact location can be accurately estimated (and it should be quite accurate if they have had the time and accuracy needed to nuke it), at a distance of 50 km from ground zero the only prep needed would be to board up windows. If the point of impact is in a major city, evacuation will still be quite challenging, and people will die from the evacuation as well as not being evacuated. But, this would be in no way as problematic as evacuating Florida.

Outside of 25 km, shelter in place measures would often be sufficient to avoid significant personal harm. A true regional disaster that will be the lead story for quite a while, but no need to evacuate the whole state.

At the time of the Fukishima disaster, 51 people died as a result of the evacuation - given the much more challenging, it is safe to assume a much larger number of people would die by attempting to evacuate Florida.

Changing the meteor characteristics to make it match the destructiveness you want to achieve can run into another problem, the bigger the rock, the sooner it will be detected. If you decide that is what you want, I suggest you user a higher speed impact (one going counter to the Earth path around the sun is a good option since that is around 30 km/s), - but the same rock hitting at 50 km/s is still has a long way to get to require evacuating the entire state.

  • $\begingroup$ If you want to have the rock not be seen until the last minute, have it come from the inner solar system where it'll be hidden in the suns glare. $\endgroup$ Jun 13, 2022 at 12:25
  • $\begingroup$ @DanIsFiddlingByFirelight - large rocks already in earth crossing orbits are actively scanned for. Sky surveys are getting better every year. The Chelybinsk meteor is a good example of solar glare that prevented detection, but rocks 150 m in diameter are considerably brighter and already subject to earlier detection. Not to mention that we are planning additional satellites in solar orbit that won't be obscured by solar glare. It's getting tougher to hit the earth with a big rock without early warning. $\endgroup$ Jun 13, 2022 at 16:22
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    $\begingroup$ Yes, we're getting a good handle on rocks that are mostly outside the Earths orbit. But while people have been talking about putting a NEO searching telescope significantly sunward for years, no one has actually done one yet. Until someone actually does so and collects several years of data, most Aten asteroids (earth orbit crossing but which spend a majority of their orbit closer to the sun) remain unknown. Until then surprise state/country killer size rocks remain possible. That's why I specified it coming from sunward because that's a blindspot for both short term detection and surveys. $\endgroup$ Jun 13, 2022 at 17:15
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    $\begingroup$ Increasing the size of the rock will mean that Florida is not the only place that you need to evacuate. Great frame challenge! $\endgroup$ Jun 14, 2022 at 15:56
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    $\begingroup$ @Michael, it had three transmitters operating at different frequencies, the most powerful of which could produce a one-megawatt continuous beam. It was used to do things like make an elevation map of Venus or measure the distance to Titan. $\endgroup$
    – Mark
    Jun 14, 2022 at 21:21

Reality bites - on paper you can move millions of people via cars and airplanes and probably one or two million by ship.

But in a panic situation, all your planning will break down rather quickly. There will be accidents on the roads blocking or slowing everything down. People will lose their tempers, cars will be filled not at optimum capacity, some idiot will go on the road with almost empty gas tank. Similar situation at the airport - people screaming, kids lost, panic, people trying to board already full planes, etc. etc.

So under real-life conditions at most at third of the maximum capacity will actually manage it.


Large majority escapes using autonomous platooning vehicles

Florida has 22 million people.. with proper coordination between state authorities and transport services some 80-90% could escape.. in the 2030's.. when energy transition plans are implemented..

Motor cycles

In 2020 there were an estimated 620,077 registered motorcyclists in Florida, when used effectively they allow about a million people to escape.

Passenger planes

As soon as the asteroid is discovered, the airlines organize a coordinated attempt to evacuate Floridians out. In a day, Miami airport can handle 1000 flights. Say 500 are outgoing, 250.000 people can be evacuated using airplanes, per international airport.

Shared autonomy driving

On the day of the disaster, the Florida government decides to open up the left side of the high ways exclusively for platooning (coordinated) shared autonomy driving north.



enter image description here

New personal transport services

In the 2030's, new vehicles will appear. As fossil fuel has become expensive, the number of public transportation-like decentralized vehicle services (driverless taxis) now far exceeds the number of private cars. These vehicles bring you to your work daily and traffic jams have disappeared. On the highways, these taxis communicate to keep distance. So a traffic jam can be prevented. Private electric vehicles will have a device that allows them to join the taxis.

enter image description here

Supposed 2030's some 75% or the fossil fuel cars got replaced, and the transportation services coordinate their efforts and each available vehicle has 2-3 people, around 14-18 million Floridians could escape.

Gasoline and diesel cars

When Floridians are lucky and listened to Greta Thunberg, on the right side of the road, the traffic jam will be prevented. Most cars are electric now. And you'd have less private cars. Estimated some 800.000 (10%) of the privately owned gasoline cars could still be operational, theoretically you'd get 1-3 million people on the road. But that part will be on the right side, subject to local accidents.. unorganized.. only some percentage will reach a safe area.

  • 1
    $\begingroup$ One issue is that driverless taxis are not expected to replace personal vehicles at a 1:1 rate - one autonomous car service can replace several personal vehicles. Instead of 15M people in 7M personal vehicles, you may need to pack 15M people into only 3M shared vehicles. If the number of shared autonomous vehicles is even lower, there aren't even enough seats for everyone at once! And how quickly and reliably can the autonomous cars be reconfigured to drive on the wrong side of the road? $\endgroup$ Jun 13, 2022 at 14:29
  • $\begingroup$ @NuclearHoagie the recognized feature on the road is the white lines and the radio contact with the other cars. It doesn't matter which side of the road. And we're talking 10 years down the line.. which is also 10 years in development.. and preferably, a democratic governor who will listen to Greta :d in short: above answer is optimistic, not pessimistic. $\endgroup$
    – Goodies
    Jun 13, 2022 at 16:06
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    $\begingroup$ Platooning pretty much requires perfect performance from every vehicle involved. With traditional driving, a single failure (flat tire, stalled engine, etc.) will cause a local disruption around the disabled vehicle; with platooning, there isn't enough room for this and an entire lane stops all the way back. Platooning has moderately better best-case performance than traditional driving, but far worse worst-case performance, and an evacuation pretty much guarantees the worst-case situation. $\endgroup$
    – Mark
    Jun 14, 2022 at 1:27
  • $\begingroup$ Ok @Mark I am not advocating platooning to evacuate all of Florida out in a single row. "platooning" is not a solution for replacing cars, that's a popular opinion lots of current car-owners advocate.. but that' kind of statistics discussions is a different topic. Platooning does prevent traffic jams, which will be the main problem in any evacuation scenario. $\endgroup$
    – Goodies
    Jun 14, 2022 at 6:16
  • $\begingroup$ What happens if you CLOSE the highways to personal vehicles entirely and use them for busses and heavy goods vehicles with trailers packed to standing room only full of refugees? Very unamerican I know, but particularly if you can bugger the speed limiters on the busses and heavy goods and organise for some fuel bowsers it should increase capacity. In the same vein, a goods train run in the manner of the Indian railways can be way more passenger dense then Amtrak. Now you WILL kill people, crashes without seatbelts, falling off trains, all that stuff, but it is a numbers game. $\endgroup$
    – Dan Mills
    Jun 14, 2022 at 16:29

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