Recently given an advance copy of the official 2008 subway passenger counts, I found myself wondering -- what would it take in terms of auto facilities to replace the morning rush hour carrying capacity of the NYC subway?

This is an important question because the cost (be it financial, environmental, etc) of building, operating, and maintaining a transportation facility is generally determined by the maximum capacity it is expected to provide. To avoid ruining any surprises, all calculations here are derived from the publicly available 2007 Hub Bound Report, and implemented in this spreadsheet. The "hub" here is Manhattan below 60th Street -- New York City's official CBD.

Just to get warmed up, chew on this -- from 8:00AM to 8:59 AM on an average Fall day in 2007 the NYC Subway carried 388,802 passengers into the CBD on 370 trains over 22 tracks. In other words, a train carrying 1,050 people crossed into the CBD every 6 seconds. Breathtaking if you ask me.

Over this same period, the average number of passengers in a vehicle crossing any of the East River crossings was 1.20. This means that, lacking the subway, we would need to move 324,000 additional vehicles into the CBD (never mind where they would all park).

What does it take to move that many additional vehicles? Well, it depends. Different auto facilities in the city appear to have different capacities (as expressed in vehicles per hour per lane):

Facility Inbound Lanes Max Hourly Inbound Traffic Veh/Lane/Hr Lanes Needed Queens Midtown Tunnel 2 3,882 1,941 167 FDR Drive 3 5,425 1,808 179 Brooklyn Battery Tunnel 2 3,017 1,509 215 Brooklyn Bridge 3 4,262 1,421 228 West Side Highway 4 4,825 1,206 269 2nd Ave 6 4,739 790 410 5th Avenue 5 1,712 342 946

At best, it would take 167 inbound lanes, or 84 copies of the Queens Midtown Tunnel, to carry what the NYC Subway carries over 22 inbound tracks through 12 tunnels and 2 (partial) bridges. At worst, 200 new copies of 5th Avenue. Somewhere in the middle would be 67 West Side Highways or 76 Brooklyn Bridges. And this neglects the Long Island Railroad, Metro North, NJ Transit, and PATH systems entirely.

Of course, at 325 square feet per parking space, all these cars would need over 3.8 square miles of space to park, about 3 times the size of Central Park. At that point, who would want to go to Manhattan anyway?

Without the NYC Subway, I'm pretty sure this is what it would look like if we provided for to everyone commute by car:

Update: people seem to be taking this map quite seriously, whereas I would call it ... conceptual. The blocks in Manhattan below 57th Street are the theoretical parking lots, whereas everything else is the additional roads, bridges, and tunnels we would need to move the cars.