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Squishy Logistics

That’s a map of Manhattan with “1874” written on it in pencil, so let’s say it’s from 1874. The vast bulk of the population still lived south (left) of Central Park, and some of the streets on the Upper East and Upper West Sides had not yet been opened. This map is worthy of note, however, because of the pencilled lines in the heavily-populated part of the city. The pencilled legend in the lower left tells us that the black lines represent “carted off” and the red lines represent “heaped.” This is (per the context of this week’s storm) a map of how the city government was dealing with snow on the streets.

First, this is a big issue today and it was a big issue then. Snow’s pretty, but there can be a lot of it. New-fallen snow has a density of 3 to 4 pounds per cubic foot (pcf); packed snow can easily get past 30 pcf. (For comparison, water is 62.4 pcf.) A midtown block is 250 feet north-south, comprising 200 feet of block front and 50 feet of a cross street (or 25 feet twice, of half of the cross-street on each side, if you’d prefer) and anywhere from 250 to 600 feet long, plus an avenue of 75 or 100 feet width. Let’s go for an average size of 250 feet by 400 feet, and snow (equal to our recent storm) of 10 inches depth. That’s 83,333 cubic feet of snow on one block, or 250,000 pounds of snow at 3 pcf. 125 tons of snow on one bock adds up pretty fast when you’re talking about a large city. Most of that snow falls on roofs or in private yards, but using a 50-foot side street and the usual 100-foot avenue, 40% of the block area is street. (It would be a smaller percentage with longer blocks or, as is true downtown, narrower streets.) That still leaves 50 tons of snow per block that’s in the public street and theoretically needs to be cleaned. And, of course, in 1874 the cleaning was done using muscle power supplied by humans and horses.

Note that compacting the snow reduces its volume but not its weight, so it makes the job easier, but not by all that much. And if it gets warm after the storm, a fair amount of snow will be lost to melting and sublimation, but if stays cold, that amount will not be much.

So what to do? In 1874, the answer was three tiered. Important streets – like Broadway, the long black right-left line – had their snow carted off. Streets of lesser but some importance – like West Street along the Hudson River, from Liberty Street to Chambers Street – had their snow heaped up. That was about the same amount of shovel labor, but eliminated the carting. And streets of low importance – the 7th Ward, where poor people lived, or South and Front Streets downtown, home to small-scale industry – got nothing. People could shovel their own snow or wait for it to melt. These days the city uses the first two categories for driving lanes, and building owners are reposnsible for clearing the sidewalks, which almost always means piling up rather than carting off.

One last detail: where do you cart this huge volume of material to? The answer today is the same as it was then: you dump the snow off a pier into the river, and let it disappear semi-naturally.