What's behind the West Coast traffic jam ...

Shipping container trucks at the port in Long Beach, Calif.
Getty Images
Shipping container trucks at the port in Long Beach, Calif.

There's a traffic jam at ports on the West Coast. There is also a tense labor situation.

How much one has to do with the other is a matter of debate.

Ship lines this week pointed a finger at the dockworkers union, claiming it was a staging a slowdown at the Northwestern ports of Seattle and Tacoma.

"Terminals that typically see 25 to 35 moves per hour were seeing as few as 10," a spokesman for the Pacific Maritime Association, the management group representing 78 ship lines and terminal operators, reported Wednesday.

The International Longshoremen's and Warehousemen's Union rejected the charge.

Read MoreWest Coast dock talks teeter

Despite the altercation, the two sides were negotiating Wednesday.

Sure, longshoremen working without a contract, which they've been doing since July, might not be full of hustle. But there may be other factors contributing to congestion too.

One is kind of labor related. Importers, worried about contract talks breaking down, are ordering more product in advance, building up inventory to guard against problems from a work stoppage.

"They've loaded up the pipeline," said Bruce Carlton, president of the National Industrial Transportation League, a group that lobbies on transportation issues of concern to major manufacturers. "Some have also rerouted to the East Coast. …We're still very much in the major shipping season and there's nervousness."

There's another problem: equipment. Those large containers of freight often have to be moved on chassis … basically a wheeled trailer. Once moved, those chassis often end up in the wrong place. It's like the shopping carts at a supermarket. They often end up all over the parking lot, instead of at the store entrance where people need them.

The same sort of problem is hitting the rail system. And there is a shortage of truck drivers, particular among the drayage outfits that shuffle loads between docks and railyards.

Why is the chassis, rail, and driver problem more pronounced this year than in previous years?

We're doing better. The economy is looking up … and so traffic is on the rise.

Congestion? Yeah, it may be a sign of problems, labor or otherwise. But it is also a sign of better times.