Who says it does? What does that address? Improving fleets has large ROI. The benefit is all the emissions from all those vehicles. The cost should be lowered

Who says it does? What does that address? Improving fleets has large ROI. The benefit is all the emissions from all those vehicles. The cost should be lowered per vehicle due to standardization, and due to professional managers, maintainers, and drivers who can handle much more complexity and deal with novel issues.