A comprehensive overhaul of U.S. trade policy, including the introduction of broad tariffs on most of the world, is roiling markets on Thursday. Among the hardest-hit sectors are transportation companies, including Union Pacific (UNP -4.13%), Forward Air (FWRD -21.55%), and Zim Integrated Shipping Services (ZIM -14.20%), all losing ground.Forward and Zim, two stocks known for their volatility, are both down more than 14% as of 11 a.m. ET, while the more docile Union Pacific is off by 4%.Reorienting shipping ...