The Dow Jones Transportation Average just fell into bear market territory.

According to some analysts, that’s a warning sign that the U.S. economy is in danger of slipping into a recession.

The Dow Jones transportation average is down more than 20 percent from its high in November, the official marker for a “bear market.”

Dow Transports, however, tend to predict more recessions than actually occur. The Dow Transports fell into bear market territory in 2016, 2018, and 2020.

The Dow Transportation Average fell 3.7 percent as of 1:30 on Wednesday.

Freight transportation sector has been a reliable leading economic indicator. A 2014 study found that a slowdown in an index of freight services anticipates broader economic slumps by about four months.