Freight volumes shrink as world economy stalls.

Freight volumes in the United States and around the world are falling, signalling tougher times for manufacturers amid escalating trade tensions and heightened uncertainty.

Freight volumes in the United States were up by just 0.8 percent in the three months from March to May compared with the same period a year earlier, according to the Bureau of Transportation Statistics.

Volumes fell year-on-year in May, for the first time in more than two and half years, according to the agency's transportation services index.

Freight is...