Getting The Hell Out Of Dodge
In 2001, Joe Sheehan, Jeremy Sato and I spent an extended weeked working on this. So for once, I feel like I have something useful to contribute! Let's talk hurricane evacuation.
The first thing to establish is the flow out of the city. How many cars will pass a given point on the road in an hour? Turn that upside down: how long from when the tip of one car passes a point until the tip of the next car gets there? That depends on the speed of the car, which tells you how quickly each car will pass, and the following distance.
Proper driving safety requires you to stay one carlength behind the person in front of you for every ten miles per hour you drive. You might not usually do this (I sure don't), but nobody's going to buy an evacuation plan that requires people to drive blatantly unsafely. More than a few accidents, and your timetable is shot to hell. Ten miles an hour is about fourteen point six feet per second. And a carlength...well, GM says my Chevy Cavalier is 180.9 inches long. Fifteen feet! That makes things simpler. That means the 'carlength per ten mph' rule is just another way of saying 'follow one second behind the car in front of you.' That's half the question.
At ten miles an hour, it takes your car a second to pass some point. So at fifty, say, it takes one fifth of a second. Let's use fifty as our assumed speed and say that it takes one fifth of a second for a car to pass and one second for the next car to come up. That's five cars per six seconds.
Five cars per six seconds is fifty cars a minute is three thousand cars per hour. If we average four people to a car, that's 12K people per hour. Major interstates have two lanes, so that's 24K people per hour per interstate, and Mapquest tells me that there are three interstates heading out of NOLA. I don't know if all of them were open or went anywhere helpful to the refugees, but let's leave that aside. Wikipedia says there's 1,337K people in the Greater New Orleans area. At 24K leaving per hour, that's a 53 hour job, easily done with the warning they had. See, that wasn't so hard!
Right.
The issues of people not having cars to leave with, money to go anywhere, or interest in abandoning their city (Thanks for the perspective, seraphyc!) are well-known. Ignore them all for now. Two huge onions in the ointment are:
Don't leave the hamster!
If people take the warning seriously, they know that everything they own might soon be destroyed, and they're going to want everything they can jam in their cars. More most families, this precludes riding four to a car, which plays hell with our numbers. Further, it means that not enough people are going to be ready to leave when the evacuation is first announced, especially if it's properly done with days to go before the storm hits. Then everyone finally gets packed and hits the road at once, which leads to:
Don't be greedy, Milton, there's time to evacuate everyone.
Look at what our plan calls for: a sustained, even flow out of the city over a period of two days and nights. That's just not gonna happen without a spectacular amount of coordination. 9 AM is always going to be a more popular time for evacuating than 2 AM. The relatively dead hours are worrisome, as precious highway capacity is being wasted. The overbooked hours are worse. We're already talking about highways packed to the point of dubious safety. What happens when you add another car? As it merges in, everyone around it slows down to avoid a crash. Then people resume speed, but with the new car occupying the space of the car that's now behind it, which is occupying the old space of the car behind it and so on and so on until you get to some other point where cars should be merging on but can't without slowing down or following too closely. The city isn't evacuated any more quickly, and there's more time wasted at the entry ramps as people look for a good opening.
If thousands and thousands of extra cars are added to the highway, everyone slows down to let the first car merge in, and then to let the second car merge in, and then the third and the fourth and pretty soon they simply can't speed up again, which gives you a traffic jam. From a flow-out-of-the-city standpoint, this is irrelevant. Cars are still passing points at the same rate (moving more slowly, but keeping less of a distance). But for the drivers it's hell. I don't need to describe traffic jams to you. I spent two hours going ten miles an hour down 90-94 the day before Thanksgiving '03, and I hope to god I never have to do that again. Now imagine eighty miles of traffic from New Orleans to Baton Rouge. It simply will not let up. Too many people got on the highway for the road to process, and that's that.
So the only possible way to evacuate a city that size is in an organized manner, possibly one neighborhood at a time. For that, you need to coordinate things through a group of people who know the city and whom the citizens will listen to. I don't know if such a group even exists in New Orleans (given the reports of police corruption), but I'm almost sure it isn't the Feds.
It's a rough problem, but that doesn't excuse what happened. If you try and coordinate an evacuation, there's a chance it will go wrong or people won't listen to you. Instead the local government seems to have shrewdly elected to hide under a pile of coats and hope that somehow, everything would work out. And who's surprised? They were picked to represent us, and we didn't give two shits about worst-scenario disaster relief until last week. So if you want to do something, learn about what needs to be done to cope with a devastated city and elect officials who have coherent plans for that scenario. Because if this is the worst destruction on American soil we see in our lifetimes, we'll have been unbelievably lucky.
The first thing to establish is the flow out of the city. How many cars will pass a given point on the road in an hour? Turn that upside down: how long from when the tip of one car passes a point until the tip of the next car gets there? That depends on the speed of the car, which tells you how quickly each car will pass, and the following distance.
Proper driving safety requires you to stay one carlength behind the person in front of you for every ten miles per hour you drive. You might not usually do this (I sure don't), but nobody's going to buy an evacuation plan that requires people to drive blatantly unsafely. More than a few accidents, and your timetable is shot to hell. Ten miles an hour is about fourteen point six feet per second. And a carlength...well, GM says my Chevy Cavalier is 180.9 inches long. Fifteen feet! That makes things simpler. That means the 'carlength per ten mph' rule is just another way of saying 'follow one second behind the car in front of you.' That's half the question.
At ten miles an hour, it takes your car a second to pass some point. So at fifty, say, it takes one fifth of a second. Let's use fifty as our assumed speed and say that it takes one fifth of a second for a car to pass and one second for the next car to come up. That's five cars per six seconds.
Five cars per six seconds is fifty cars a minute is three thousand cars per hour. If we average four people to a car, that's 12K people per hour. Major interstates have two lanes, so that's 24K people per hour per interstate, and Mapquest tells me that there are three interstates heading out of NOLA. I don't know if all of them were open or went anywhere helpful to the refugees, but let's leave that aside. Wikipedia says there's 1,337K people in the Greater New Orleans area. At 24K leaving per hour, that's a 53 hour job, easily done with the warning they had. See, that wasn't so hard!
Right.
The issues of people not having cars to leave with, money to go anywhere, or interest in abandoning their city (Thanks for the perspective, seraphyc!) are well-known. Ignore them all for now. Two huge onions in the ointment are:
Don't leave the hamster!
If people take the warning seriously, they know that everything they own might soon be destroyed, and they're going to want everything they can jam in their cars. More most families, this precludes riding four to a car, which plays hell with our numbers. Further, it means that not enough people are going to be ready to leave when the evacuation is first announced, especially if it's properly done with days to go before the storm hits. Then everyone finally gets packed and hits the road at once, which leads to:
Don't be greedy, Milton, there's time to evacuate everyone.
Look at what our plan calls for: a sustained, even flow out of the city over a period of two days and nights. That's just not gonna happen without a spectacular amount of coordination. 9 AM is always going to be a more popular time for evacuating than 2 AM. The relatively dead hours are worrisome, as precious highway capacity is being wasted. The overbooked hours are worse. We're already talking about highways packed to the point of dubious safety. What happens when you add another car? As it merges in, everyone around it slows down to avoid a crash. Then people resume speed, but with the new car occupying the space of the car that's now behind it, which is occupying the old space of the car behind it and so on and so on until you get to some other point where cars should be merging on but can't without slowing down or following too closely. The city isn't evacuated any more quickly, and there's more time wasted at the entry ramps as people look for a good opening.
If thousands and thousands of extra cars are added to the highway, everyone slows down to let the first car merge in, and then to let the second car merge in, and then the third and the fourth and pretty soon they simply can't speed up again, which gives you a traffic jam. From a flow-out-of-the-city standpoint, this is irrelevant. Cars are still passing points at the same rate (moving more slowly, but keeping less of a distance). But for the drivers it's hell. I don't need to describe traffic jams to you. I spent two hours going ten miles an hour down 90-94 the day before Thanksgiving '03, and I hope to god I never have to do that again. Now imagine eighty miles of traffic from New Orleans to Baton Rouge. It simply will not let up. Too many people got on the highway for the road to process, and that's that.
So the only possible way to evacuate a city that size is in an organized manner, possibly one neighborhood at a time. For that, you need to coordinate things through a group of people who know the city and whom the citizens will listen to. I don't know if such a group even exists in New Orleans (given the reports of police corruption), but I'm almost sure it isn't the Feds.
It's a rough problem, but that doesn't excuse what happened. If you try and coordinate an evacuation, there's a chance it will go wrong or people won't listen to you. Instead the local government seems to have shrewdly elected to hide under a pile of coats and hope that somehow, everything would work out. And who's surprised? They were picked to represent us, and we didn't give two shits about worst-scenario disaster relief until last week. So if you want to do something, learn about what needs to be done to cope with a devastated city and elect officials who have coherent plans for that scenario. Because if this is the worst destruction on American soil we see in our lifetimes, we'll have been unbelievably lucky.