In Plans to Evacuate U.S. Cities, Chance for Havoc - New York Times:

"New York, more than most American cities, has the advantage of a sprawling mass transportation system. Eight million people a day use the system, and officials count on it to be useful in an emergency as well. That could be vital, because city traffic, already a problem in an ordinary rush hour, would pose a significant challenge.

"Police Commissioner Raymond W. Kelly said the city has two general evacuation plans, one for hurricanes and another for terrorist attacks. The plans include the opening of hundreds of shelters, mostly in schools. But officials acknowledge that many elements of an evacuation would have to be improvised."

Leave aside for the moment the airy notion that millions of evacuees can be accommodated in hundreds of shelters (i.e., on the order of 10,000 evacuees per shelter), and let's give this idea of evacuating New York City for a hurricane a test drive.

Start with the comforting thought that the transit system serves eight million riders daily and that eight million is approximately the population of the city. But a high proportion of those eight million riders are city residents going from one point in the city to another. The subway portion of the transit system doesn't leave the city at all.

Only one of NYC's five boroughs is on the mainland of North America. The other four cover two large islands and a small part of a very much larger one. This means there are a relatively few bridges and tunnels by which trains, buses or cars can exit. On the positive side, unlike most of the barrier islands on the Gulf and Atlantic coasts, Staten Island and Manhattan Island are not low-lying sand bars. The highest point of land on Manhattan is well over 200 feet - a far cry from Galveston.

The other thing in New York's favor in a hurricane scenario is that much of the architecture is stone, brick, concrete and steel; and, athough there are many neighborhoods of wood frame housing, especially in the outer boroughs, you don't have mile after mile of highly vulverable mobile homes as you do in much of the South. So maybe a lot of New Yorkers, including nearly all of Manhattan, can shelter in place and others can be accommodated in shelters in the city.

Now, let's go back to the bad news. In a hurricane so severe that the city, or even just the lower elevations and more vulnerable structures, must be evacuated, won't Nassau and Suffolk counties (the middle and eastern portions of Long Island) also need to evacuate? That adds around three million more people joining the exodus. And, aside from the ferry service to New London, CT at Orient Point (which will probably be committed to the evacuation of Plum and Fisherman's islands in NY and Block Island, RI) and another from Port Jefferson to Bridgeport, CT, the only ways out by rail or highway go through the Borough of Queens.

From Queens, there are three bridges to the Bronx, and three ways into Manhattan, although that may not be very useful as an evacuation route since there are only three routes from there to New Jersey and one highway and half dozen surface street connections to the Bronx. Or you can continue your drive into Brooklyn from which there are four entries to Manhattan and one bridge to Staten Island from which there are three ways one can get to the mainland in New Jersey.

Leaving out the handful of surface street connections from Manhattan to the Bronx, we have a total of eight highway bridge or tunnel connections as choke points for any evacuation of Long Island. Pulling everyone out of seven counties puts about a million people on the average bridge out of town even leaving out the Bronx which is part of the mainland and has a dense network of surface connections into Westchester Co. in addition to five major highways which will be clogged with folks evacuating from the island counties to the south. We can also leave out Staten Island in this analysis since whatever LI traffic comes across the Verazzano Narrows Bridge can continue into NJ using one highway, leaving two or three other routes open for the less than half million people on SI.

Assume that 25 percent will get out by rail, air and ferries, that leaves about 6 million and if most of Manhattan and parts of Brooklyn and Queens can shelter in place, maybe we can get down to only 4 million people on the highways. At a very optimistic equal numbers of cars carrying four people and buses carrying 40 people that puts about 44 people which, moving at even a slow speed takes up about 80 feet or around 2800 people per lane mile. At 30 mph (too optimistic) that moves 84,000 people per hour in one lane and, if there are 40 lanes available, we get over 3 million people out in an hour, except that can't happen from a standing start.

Average occupancy of cars will be less than 3, there will be more than 80,000 of them and we won't have 80,000 buses. MTA New York City Transit claims a fleet of 4566 buses serving 2.5 million riders daily in the five boroughs. There are other bus fleets serving the city, but this would be the largest source available for evacuation.

More reasonably, we get one million cars with 3 million people and we rustle up 10,000 buses to make three trips each to points in the suburbs. And, based on Houston's experience we expect them to move very slowly. This gets us about 1000 persons per lane mile leaving town and at 5 mph it takes at least 20 hours to get them all to the mainland, and substantially longer until they have reached shelters. But we likely won't have that many lanes leaving town, since some must be kept open to allow buses in for additional trips, to allow movement of ambulances in and out ferrying out some of the sick and injured, and to allow access to provide gas for cars that run out while caught in all day traffic jams, fire trucks to put out engine fires, cops to stop fights caused by fender benders, etc.

I'd be very interested to see how much time the actual NYC hurricane evacuation plan is expected to take, how many people are expected to participate, what mix of vehicles will be involved, and (most of all) where they plan to put all those folks when they get them out of town. I hope we never have to watch that plan collide with reality.