Time as a Trade Barrier
利用美国进口数据，分析出口商在空运和海运之间的选择，估计出运输中每一天相当于0.6%至2.1%的从价关税，对研究贸易成本和供应链管理的学者有参考价值。
A large and growing share of world trade travels by air. We model exporters' choice between fast, expensive air cargo and slow, cheap ocean cargo, which depends on the price elasticity of demand and the value that consumers attach to fast delivery. We use US imports data that provide rich variation in the premium paid for air shipping and in time lags for ocean transit to extract consumers' valuation of time. We estimate that each day in transit is equivalent to an advalorem tariff of 0.6 to 2.1 percent. The most time-sensitive trade flows involve parts and components trade.