Rising cargo volume at the Port of Charleston has brought with it an unintended consequence: a shortage of the trailers that truckers need to haul shipping containers.

The State Ports Authority said this week it's investigating complaints about the availability of usable chassis. The shortage has been blamed for delaying some shipments at the Wando Welch Terminal in Mount Pleasant and North Charleston Terminal.

"We are investigating the truckers' recent comments that damaged chassis are not being repaired in a timely manner, causing delays for truckers while chassis are repaired ...," said Jim Newsome, president and CEO of the SPA.

A few years ago, ocean carriers like Maersk sold off their chassis businesses to save money. That has meant the pooled equipment has been maintained by third-party groups, which replace worn tires and brakes and burned-out lights.

"Ultimately, the chassis pool operator, who in this instance is Consolidated Chassis Management, bears the responsibility for the management of chassis repairs," Newsome said. "If we find these comments to have merit, we will not accept this practice and we will seek prompt corrective action."

Newsome's response follows recent discussions involving the SPA, trucking industry leaders and the company.

Phil Wojcik, president and CEO of Consolidated Chassis, said Tuesday that the Budd Lake, N.J.-based company is taking measures to resolve the problems.

That includes adding more mechanics, employing vendors on overtime to catch up with repairs, streamlining the repair approval process, and removing damaged chassis from local port terminals.

Wojcik said the problems at Charleston area terminals are due in part to cargo growth.

"There has been an increase in the amount of loads through the Charleston area, and it continued through the cargo surge" at the beginning of the year, Wojcik said in an email. "This surge has created a higher than usual return of chassis needing maintenance."

He added that weather conditions have also delayed some repairs. Frequent rain cuts the mechanics' productivity in the yard and slows the entire process, Wojcik said.

"Our out-of-service levels are kept to a minimum, in particular compared to other regions of the U.S. where chassis issues are more prevalent," he said.

Keith Johnson, president of the Charleston Motor Carriers Association and owner of H&J Trucking, said local chassis shortages aren't unusual, but they have worsened in recent months.

Johnson said part of the problem was the harsh winter prompted vessel owners to divert ships to Charleston instead of original destinations like New York.

"All of that cargo ended up down here and all of a sudden we had a lot of extra containers to get delivered. That has been piling up, and it just created a chassis shortage where truckers were having to grab chassis that were in need of repairs," he said.

Earlier this month, the SPA reported that it handled a total of 692,338 containers of all sizes since its fiscal year began July 1, up nearly 5 percent.

The situation has forced some drivers to scour terminals for workable chassis or wait for repairs, Johnson said.

"Drivers don't want to be using their limited time tied up for an hour or two in the port," Johnson said.

Some trucking operators have been buying their own fleets of chassis to lessen the chances of problems with equipment in the pool. That includes Hunter Transportation and Bulldog Hiway Express.

"We have invested and purchased chassis equipment for much of our needs," said Phil Byrd, CEO of North Charleston-based Bulldog Hiway Express and chairman of the American Trucking Association. "This has lessened the chassis shortage for us, but there is a shortage that will continue to worsen as volumes increase."