City Filth, Decoded: The Gunk on Subway Platforms Actually Has a Name

Posted On Wed, February 24, 2016 By

Posted On Wed, February 24, 2016 By In City Living, Transportation

Image: Xymox/Flickr

Do you ever wonder what that black schmutz that collects on the subway platform is? Has all the discarded chewing gum in the world begun to mobilize? What if I put my bag on it? Slate’s What’s That Thing column appropriately examines the phenomenon: After repeated unreturned phone calls to the MTA, the intrepid journalists got “Gridlock Sam” Schwartz and his transit gurus on the case.

Finally the fine folks from the MTA rallied and gave name to the mysterious muck. According to NYC Transit assistant chief of the Division of Stations Branko Kleva, the stuff is mastic, a tar-like substance used to seal and waterproof the subway tunnels. When it heats up, (in the summer, for example, ironically from the heat generated by subway car air conditioning) it starts to “flow and drip down from the roof of the tunnel onto the platforms below.”

subway gunk 1 Image: Diego Torres Silvestre via flickr.

Slate further grosses us out: “In fact, you can often see stalactites (Greek for ‘that which drips’) of mastic forming on beams or structures right above the platform areas” where there’s a puddle of the stuff. It’s apparently unrelated to the mildly frightening “subway juice” that occasionally drips on the unsuspecting during rainy days (though that’s likely similar to the “building juice” found above ground dripping from scaffolding, which is a whole other can of worms.). The mastic actually seals the cracks, which keeps drips out, so evil points withheld for that. MTA officials say the stuff is benign, anyway, so you can go back to worrying about the germs on every available surface.

pigeon and subway gunk A subway filth two-fer. Image: Susan Sermoneta/Flickr

The only way to remove the sticky stuff from platforms is to “scrape them off, or powerwash them.” In this case the reporter found that his prime subject had been carefully scrubbed when he returned for further investigation, which means it is actually possible for the subway to get cleaner rather than dirtier, and that may be the real story here.

[Via Slate]


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