The shipping industry, which serves as the arterial system for the economy, is feeling the chill of a slowdown.

As U.S. growth decelerates, an overwhelming majority of trucking companies tracked by Merrill Lynch expect shipping rates to either fall or stay flat, the firm said on Friday, as its Truckload Diffusion Indicator tumbled to its weakest levels since October 2016.

The index, a barometer of the freight-hauling industry, is now down 29% year over year, and shippers’ outlooks are broadly negative to neutral.

One Southeast shipper surveyed by Merrill noted that current conditions in Florida were “the quietest he has seen it in his 20 years in Florida through May and June.”

The bank also reported that asset based companies in the region “are lowering prices to compete with the spot market, and expects this situation to level out in the next month or so.”

Merrill’s anecdotal data shone a light on a critical sector of the U.S. economy, where ominous signs suggest a slowdown may metastasize into something deeper — especially with the U.S. and China engaged in a trade war that shows no signs of an immediate resolution.

The sluggish conditions cited by Merrill Lynch in its report appear to be playing out around the country. The Cass Freight Index, watched by some market analysts as a bellwether of the broader shipping industry, fell for the fifth straight month in May.

Meanwhile, with shipments tumbling 6% from the year prior, Cass Freight sees conditions moving from “‘warning of a potential slowdown’ to ‘signaling an economic contraction.’”

Cass Freight warned that “weakness in spot market pricing for many transportation services, especially trucking, is consistent with the negative Cass Shipments Index and ... strengthens our concerns about the economy and the risk of ongoing trade policy disputes.”

In March, shipping and logistics giant FedEx lowered its outlook for the year, citing “weaker global trade trends” — and analysts are holding their breath when the company reports quarterly earnings next week.

Javier is an editor for Yahoo Finance. Follow Javier on Twitter: @TeflonGeek

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