(Bloomberg) -- The biggest US ports are stretching capacity limits and need to expand to handle anticipated growth in inbound shipping, according to shipping industry veteran John McCown. 

Even before the Baltimore bridge disaster that shut one of the East Coast’s most important delivery points, space was so constrained at the nation’s 10 largest ports that containers unloaded from ocean-going vessels were being stacked six high in some places, said McCown, founder of Blue Alpha Capital and former CEO of Trailer Bridge Inc. 

The stacks can’t go any higher without threatening to crack pavements below, he noted.

“Capacity limits are closer than most people think,” McCown said Tuesday at the Port of the Future conference at the University of Houston. “Our container system is approaching its physical limits.”

Read More: Baltimore Disaster Has Other Ports Racing to Absorb Cargo

Over the next 20 years, the US will need to expand inbound shipping capacity by the equivalent of four Ports of Los Angeles, said McCown, a senior nonresident fellow at the Center for Maritime Strategy.

“Inbound traffic will continue to grow,” he said. “We need to take steps now.”

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