The growth thesis for heavy-duty truck sales continued to play out in May. Net orders climbed by 84% from May of 2009.

That growth thesis says that truck sales should boom in late 2010 and into 2011 as truck owners, who have put off buying during the recession, resume purchases driven by growth in shipping volumes, new government rules that require reduced pollution, and improved engine technology that increases performance and lowers operating costs.

More than 50% of orders for Class 8 trucks placed in May are scheduled for delivery in the third quarter, just in time to beat the surge in volumes that comes with the peak fall shipping season, according to ACT Research. In June the analyst of truck and commercial vehicle markets increased its forecast for heavy-duty truck production in 2010 by 23% over 2009 levels.

Orders for medium-duty trucks (Classes 5-7) were also up in May—by 33% from May 2009. Orders for these classes of trucks have been growing more slowly than for heavy duty trucks because end markets among home builders and highway construction contractors have been very slow to recover from the recession—and in many areas of the country aren’t showing any signs of recovery at all.

All this should help Cummins (CMI). Wall Street analysts have raised their estimates for the company’s second quarter earnings in the last month to 87 cents per share from 82 cents. Earnings of 87 cents a share would be an increase of 189% from the second quarter of 2009.  For all of 2010 analysts are projecting earnings growth of 55% from 2009 levels.

As of July 8 I’m going to raise my target price a tad to $80 a share by March 2011 from the prior $79 a share by March.   

Full disclosure: I own shares of Cummins in my personal account.