North American orders for Class 8 semi-trucks jumped 92 percent in September as trucking companies continued to struggle with tight capacity in a booming U.S. freight market, FTR, a company that tracks the industry, said on Wednesday.

September was the 10th best month ever for North American sales of big rigs and capped the highest-ever quarter for sales.

Preliminary orders for the big 18-wheelers that haul freight along the highways of the United States, Canada and Mexico reached 42,300 trucks, up 92 percent from 22,082 in September 2017.

The tight U.S. freight market means many rail and truck customers are grappling with how to defend profit margins as transportation costs continue to climb.

"The economy is surging right now, putting stress on shippers to find trucks to deliver goods on time," Don Ake, FTR's vice president of commercial vehicles, said in a statement. "Fleets don't want to be stuck in the same situation next year, so they are placing huge orders for trucks well ahead of time."

"Demand, as indicated by the surge in orders, will be even stronger next year," he added.

Full-year 2017 orders for Class 8 trucks came in at 290,000 units, compared with 164,000 in 2016. The United States is by far the largest market in North America.

Over the last 12 months, orders for semi-trucks have totaled 497,000 units.

The main truck makers in the U.S. market are Daimler AG , Navistar International Corp, Paccar Inc and Volvo AB.