COLUMBUS, Ind. — Continuing the trend of one step forward, two steps back, North American heavy-duty truck net orders fell 50% in November compared to October.

That’s according to the latest data compiled by ACT Research. A total of 10,550 Class 8 units were ordreed in November. ACT says October’s numbers were inflated by a pre-buy in advance of costly EPA2010 emissions standards.

ACT’s latest State of the Industry: Classes 5-8 Vehicles, showed that November’s Class 8 orders were actually consistent with the past six months, with the exception of October. November’s figures were down 7% year-over-year.

Medium-duty orders, meanwhile, were down from October but up 40% over November, 2008.

“October’s surge in heavy-duty truck orders had little staying power, as the strong orders filled most of the remaining pre-EPA2010 emission mandate build slots,” said Kenny Vieth, partner and senior analyst with ACT. “Medium-duty orders, while down from October, continued to be relatively strong. We assume much of the strength in the medium-duty segment is related to body-builders booking pre-mandate chassis so that they will have more cheaply priced units to sell through 2010.”