More than 40 percent of retailers and manufacturers plan to shift volume to east coast ports as a result of chronic west coast congestion, according to an American Shipper research report.

The report, a poll of 400 shippers and 200 logistics providers, explores manufacturers' and retailers' responses to west coast congestion as well as the attitudes of shippers large and small, including 3PL cargo allocation plans and distribution centre strategies.

"Port congestion on the west coast the past nine months has had an indelible effect on shippers," said American Shipper research chief Eric Johnson.

"It's clear many shippers and 3PLs are rethinking how to structure their supply chains so they're less vulnerable than they have been over the past year. For a sizable percentage of respondents, that means shifting cargo to east coast ports, and even relocating to new distribution centres on the east coast."