What goes around comes around: Export-enhancing effects of import-tariff reductions
研究发现，由于运输公司需承诺足够运力应对最大货运量，拥有市场势力的运输公司会在进口关税变化时策略性调整运费，导致进口国削减关税后出口也增加。基于1995-2007年全球数据，关税每降1%，进口运费涨约0.8%，出口运费降约1.1%，出口量增0.6%-1%。
In international trade, transportation requires a round trip for which a transport firm has to commit to shipping capacity that is sufficient to meet the maximum shipping volume. This may cause the "backhaul problem." Trade theory suggests that, facing the problem, transport firms with market power adjust their freight rates strategically when import tariffs change. As a consequence, a country reducing its import tariffs may experience an increase in exports as well as imports. Using worldwide data covering 1995–2007, we find evidence that supports these predictions: a 1% reduction in an importer's tariffs increases the import freight rates by around 0.8%; decreases the export freight rates by around 1.1%; and increases the export quantity by 0.6% to 1%. These findings indicate a new mechanism through which import-tariff reductions lead to export expansions.