The ecology of our environment has recently been of great concern to all of us. In the bus business, we have gone from horse drawn carriages, to electric, to steam power to diesel power to obtain an efficient, clean operating vehicle. A great deal of effort has been expended in determining the components of the emissions of the diesel engine. Great strides have been made in reducing these emissions. GMC Truck & Coach has developed and released an Environmental Improvement Program that reduces smoke to the invisible range and meets Federal standards for HC, CO and NOx. Odor also is eliminated as a problem.