REDFORD, Mich. Detroit Diesel has decided to say good-bye to most of the motorcoach industry.

The No. 1 supplier of engines to the over-the-road bus industry since, well, almost forever has decided it will no longer sell its engines to any bus builder it doesn't own.

Right now that means that starting in 2010 the only new motorcoaches sold in North America that will have Detroit Diesel engines will be Setras. That's because Setra is part of Daimler Buses North America, a unit of Daimler AG, which also owns Detroit Diesel.

Prevost Car, Motor Coach Industries and Van Hool no longer will be able to provide Detroit Diesel engines in their over-the-road buses.

While Detroit Diesel's decision, which wasn't announced by Detroit Diesel but by Prevost Car, seems startling on its face, its not a total shocker.

Since Detroit Diesel was purchased by DaimlerChrysler eight years ago, it has been considered possible Daimler might one day turn off the engine spigot. After all, the thinking went, engines produced by a subsidiary of Daimler were powering coaches that competed directly with buses made by other Daimler companies.

But other, perhaps more important, factors were at play as well.

2010 is another watershed year for diesel engines. While there has been a lot of attention paid to 2007 engines and their stricter emissions requirements, the 2010 diesel engine emissions rules are exponentially tougher.

The regulations are so stringent that Detroit Diesel spent $1.5 billion to develop a brand new engine to meet the 2010 requirements rather than modify the Series 60 to comply.

However, adapting the new engine to a wide range of motorcoach platforms would have added even more costs and the payback would have been slow.

The fact of the matter is that the motorcoach industry is a fly on the elephant that is the on-highway engine market. In a decent year, the North American motorcoach industry consumes 2,400-2,500 diesel engines. There are individual trucking companies in the U.S. that buy that many engines in a couple of years.

That is the fundamental reason why Caterpillar and Cummins have run hot and cold on the coach industry over the past 20 years. But, as of today, with Detroit Diesel bailing out, those two engine makers have the inside track to become the industry's leading power plant suppliers, with Prevost Car using engines built by its parent company, AB Volvo.

Prevost has been busy for months building a service network for its coaches equipped with Volvo engines.

And MCI, for the better part of a year, has been emphasizing the availability of Cummins engines in its coaches, along with Cat. And Van Hool has a long relationship with both Cummins and Caterpillar.

Caterpillar is the standard engine in BCI Falcon coaches and Blue Bird over-the-road buses.

When Prevost announced last month it had been notified by Detroit Diesel that Daimler AG planned to discontinue selling engines to companies outside the Daimler family, the Canadian coach builder said it had received assurances from Detroit Diesel that it would fully support all Prevost vehicles equipped with Detroit engines "now and in the future." Prevost noted it had even signed agreements with Detroit Diesel to that effect.

"It is unfortunate that Daimler has decided to take some of the choices away from coach owners and operators in North America," Prevost added.

Detroit Diesel even has cancelled its booth space at Motorcoach Expo 2009 in Orlando.

Prevost said that as a consequence of Detroit Diesel's decision it was accelerating its strategy "to offer Volvo engines to the various coach markets we serve.

"Prevost is in a unique position among bus manufacturers in North America due to the fact our parent company is AB Volvo. Volvo is the leading heavy-duty diesel engine manufacturer in the world," Prevost noted.

Bryan Couch, vice president of product development at MCI, said his company is committed to providing its customers with the broadest choices of powertrain combinations "to safeguard market fluctuations and provide operators with the best technology the market offers.

"We will continue to do our part to ensure that our customers' needs are met while working within the global dynamics of an ever evolving marketplace. With the successful launch of the industry's widest offering of powertrain combinations that meet the 2007 EPA requirements, our energies are now focused on meeting this challenge with our engine suppliers for the 2010 emission standards, which are even more stringent.

"MCI is also the first coach manufacturer to offer a hybrid alternative with first deliveries going to the Houston Metro transit authority, using the Cummins/Allison combination. We anticipate growth in application of this fuel efficient powertrain combination."

Some observers believe the 2010 emissions standards could trigger additional fallout -- of the Detroit Diesel nature -- during the next couple of years.

At the same time, the engine equation in buying a new coach appears to have receded in importance in recent years as all engines have become more bullet proof. There undoubtedly will be operators that buy a particular coach based on engine availability, but not as many as in the past.