Abstract
Container ships travel between a fixed set of origins and destinations in round trips, inducing a negative correlation in their freight rates. I study the implications of this round trip effect on international trade and trade policy. I identify this effect and develop an instrument using it to estimate the impact of transport costs on trade. I simulate counterfactual import tariff increases in a quantitative model and quantify the importance of endogenizing transport costs with respect to this effect: an exogenous transport costs model predicts a trade balance improvement from protectionist policies, while the round trip model finds the opposite. (JEL D22, F13, F14, L92, R41)