Many products sold on online platforms have additional features. Platforms can deliberately shroud these features from consumers, e.g. by revealing them only late in the purchase process. For example, platforms often reveal shipping- and handling fees, or upgrades like luggage or hotel services...

We study road congestion as a mechanism design problem. In our basic model we analyze the allocation of a set of drivers among two roads, one of which may be congested. An additional driver on the congestible road imposes an externality on the other drivers by increasing their travel time. Each...