Musings

The purpose of this post is to let people think of the practical aspects of
emptying a small city,  of say one million people.

(If there is a train then this can be used also, but since the U.S. is
a car country. I will use roads for the evacuation.)

Lets think about what you need.  A road and transport.

Assume the goal is to move people 400 miles away.  If you can get the traffic to move at
50 miles an hour.  This journey  means  driving  for 8 hours to reach the destination.

If a car is used and it has 4 people then assuming the cars are spaced 2 seconds apart,
you will have 2000 cars passing a post in the road each hour. So you can  move (2000 x 4 =) 8000 people out of the city on one lane every hour.

To evacuate a city with a million by car and assuming you have 10 lanes leading out of the city you will have to move 10 x 8000  = 80,000 people per hour.
 


So in 10 hours you can move out 800,000 people ASSUMING
1. you maintain the flow.  2 you have no traffic jams
3. no breakdowns.

This also means that you will have to have 200,000 cars.

What if you use buses?  A bus can carry  50 to 80 people.
As the bus carries 80 people  but takes up the length of road that 4 cars would take
this will allow you to take out  5 times more people per lane.
This shows that using buses to move out people is definitely  possible.
If one uses buses then you have to consider having a path for the buses to
return to collect more passengers.  Note that the trip is 18 hours so find drivers
would be a requirement.  Perhaps each bus would have 2 drivers who whould switch every few hours.
One problem is finding the buses.   In an emergency situation I think that the
state could arrange to have the buses used.

Assume that you can get 1000 buses and use these to ferry the people out.
The buses will carry 80,000 per trip. But since the round trip is 16 hours, this means
using buses will only allow you to move 100,000 people per day.
So it you take 10 days to move people out using only buses.

One problem that arise using buses is how much luggage can be carried.
It also means that some  reception centre must be used to house the
people. (When those leave by car they can find places to stay over a wide
area.)

So I think that one has to use cars to move a majority of the people out.

I think it also means that you have to convert most of lanes leading from the city
to flow out from the city. i.e. turn around the lanes.

(One may have to stop people entering the highway unless the road speed is 50 mph as
other wise you run the risk of having the people stopped on the highways.)

Now that is apparent that you can move the people out - the evacuation decision must be made
 3 to 5 ways before the storm comes if you are to ensure that the traffic flow is
to be maintained.

One also must ensure that there is sufficient gas available for the journey.

The solution might be to ensure that you have adequate fuel at locations, say 200 miles from the
city.  

How much fuel?   Assuming that average car gets 30 miles per gallon,
so you have need 12 gallons per car and there are 250,000 cars.
So this evacuation will require 3 million gallons.   The police and other services will
need about 10% - an extra 300,000 gallons.  So you need 3,300,000 gallons of fuel.

So you might want to estimate the capacity of all the gas stations in and around the
city so see how much fuel will be needed.
(As a simplification I have assumed all vehicles use gas, and ignored vehicles using diesel).

If there are are points that I have missed please make suggestions.