Someone should remind Michael Bloomberg that free does not always mean free lunches.

The billionaire New York City mayor recently rolled out a transit proposal that sounds too good to be true – probably because it is.

In order to speed up the pace of Manhattan’s famously slow crosstown buses, mayor Bloomberg suggested eliminating the $2.25 fare on a few of the buses, as it would put an end to all the time passengers spend fumbling for their MetroCard and cash at the bus door. It would mean free bus rides for all, but without much additional cost to the city, he reasoned, since the majority of crosstown passengers are already riding for free, using their MetroCards to transfer from the subway. If we aren’t charging folks anyway, it’s not a big money loss, is the gist of his claim.

In short: win-win.

Except, there’s a flaw to his argument. If bus fare falls to zero, it’s likely that more people (many more people) will start riding the bus, which will lead to even worse congestion and potentially require the city to spend on introducing more buses.

In other words, mayor Bloomberg is harboring under the assumption that demand for the cross town bus will not change as the price drops. In all likelihood, however, the number of bus-riders will go up dramatically because free is exciting. In fact, according to our research on free, such a change will cause many people who now walk a few blocks, to switch their ways and hop on the free bus.