Last year U.S. ports handled 20.8 million TEUs, or units equivalent to one over-the-road trailer, down from 31% from 2007.

FORBES: Recovering Economy? Not If You're Counting Truckloads

Six of the world's 10 busiest ports are located in China, when measured in terms of cargo shipped in standard containers, or TEUs (20-foot equivalent units).

FORBES

Rather, we count the numbers of TEUs moving through the port facilities around the world as the true signal of economic strength or weakness, and those numbers are rising, not falling.

FORBES: The Baltic Dry Index and Goodhart's Law

The biggest ships in use at the moment can carry around 15, 000 containers (TEUs or twenty foot equivalent units) but in 2013 ships capable of carrying 18, 000 containers are due to arrive.

BBC: Felixstowe opens new berths for giant container ships

The number of TEUs (the large containers on ships: twenty-foot equivalent units) moving through the ports of Los Angeles and Long Beach is up 23% in May year-over-year and up 26% since the beginning of the year.

FORBES: Short-Term Skepticism, Long-Term Optimism