What is the best way to transport a small three-tiered cake on the subway?

Transport layers seperate in cake boxes and assemble on site.

Subway would be pretty risky. It's not the subway itself, it's the stairs up and down. I don't know how you would do that for a 3-tier by yourself. Agree you should take a cab (with another person for assistance) and add or expense the cost. Even in a cab, sitting with a cake on your lap is not an easy thing - definitely need another pair of hands and tell the driver to stay away from those potholes.

The the cab is a good idea! But be sure to support your layers. Before you frost, put in cake dowels or at least skewers (3 or 4) through your layered cake. This will help create some structure so that the layers won't slide off each other. Then frost. Remove them when the cake is being cut for serving.

Consider taking a taxi, hold the cake on your lap, and add the cost to the cake.

Cab it, expense it.

How big is this cake? Dimensions?