Orders of medium-duty vehicles surged in January and reached their highest level since the middle of 2006, according to ACT Research.

Class 5 to 7 orders increased 39% to 31,700 during the month compared to January of 2017. Class 8 orders also surged with a 121% increase to 49,100 units over a year ago. It was the second-best month after March of 2006 since the firm began tracking. That month saw a "prebuying frenzy ahead of EPA 2007," said Kenny Vieth, president and senior analyst.

"The medium duty market experienced a high-side breakout of its own in January, with North America net orders rising to their highest level since mid-2006, and all the month’s strength derived from the truck market," he said.

The order strength may be a result of operators ordering in anticipation of a tax windfall and dealers adding inventory in expectation of windfall purchasing, Veith said in a research note.