The buses were powered by conventional diesel or natural gas engines using either V-drive or T-drive transmission couplings, with the exception of an articulated electric trolleybus variant manufactured for a single customer, the San Francisco Municipal Railway.

For example, a New Flyer D40-88 is a 40-foot (nominal) rigid high-floor bus with conventional diesel power, built in 1988.

After this time, no suffix was added to the model number, while buses from the Low Floor series, which were introduced in 1991, did have LF for a suffix.In recent time, some listings or fleet rosters may show HF as a suffix for these high floor buses.

This was a creation of public transit fans to commonly refer to these pre-low floor models.

[10] The first deliveries of natural gas-powered variants occurred in 1995: BC Transit, Los Angeles County Metropolitan Transportation Authority, and San Diego Metropolitan Transit System for the C40; Sun Metro (El Paso) for the L40.