Make the Subway Grate Again

Last winter, I was walking around the blustery streets of New York in the middle of December. It was relatively warm in the morning, but by sunset the temperature dropped precipitously and I was significantly underdressed. Walking down the street, shivering, I noticed that some of the subway ventilation grates on the sidewalk released gusts of warm air. Once I realized this, I began leapfrogging from grate to grate, spending a few moments at each to warm up before darting to the next one. I was not a party to the transaction, yet I certainly benefited from the fact that the subway cars below me were running and producing heat. Clearly, the heat coming up from the grates constitutes a positive production externality.

This summer, while walking to lunch under the sweltering sun I again passed over one of these vents and my opinion of them shifted dramatically. Whereas in the winter these vents provide a much needed respite from the cold, in the summer they make the already stifling sidewalk that much more unbearable. Instead of a positive production externality, the heat coming out of the grate was a negative production externality.

This complicates the situation significantly. The implications of internalizing the externality would depend on the time of year (or even the day-to-day weather conditions). Aside from the fact that it would be practically impossible to charge or credit whoever walks near one of the grates, the party being compensated would change periodically regardless of who’s assigned liability by the law.

It turns out that the MTA has decided to do away with the grates altogether in their new projects, removing their associated positive and negative production externalities (Note that there were other negative production externalities that accompanied these grates, such as the tendency to collect dropped jewelry and break women’s high heels, which I have not accounted for in this analysis). On the newer lines (such as the second avenue subway), hot air is instead vented out of mechanical ventilation towers.