I have been paying particular attention to the monthly report of the American Trucking Association, to compare its performance with rail, which has been sagging since the beginning of this year. A few other people are relying on the Cass Freight Index, but since that includes international shipping and air transport, it does not exclusively measure the US economy.
In April this index rose 7.7%, and was up 7.4% YoY as well. In May it gave almost all of that back:
According to the ATA, truck traffic declined 6.1% in May, and is now up only 0.9% YoY.
The trend remains neutral to slightly positive, in contrast to rail, suggesting that overall the economy, at least as measured by transport, has slowed down substantially but not yet rolled over.