If we take the fleet as being 6,200 buses (annual accounts 2016), then you can look at it two ways.
Keep the fleet in a 'steady state' and reduce the annual order from 413 to 364 buses. (6,200 / 15 years or 17 years expected life).
Or keep the annual order at 413 buses but take a two year investment holiday.
A combination of the two would appear to be what is happening, on the quiet. Hopefully investors / financiers won't notice!
If your strategic plan is to exit, or at least withdraw substantially from weaker market areas, reducing the order size to meet your expected future fleet size rather than your current fleet size is sensible.
I'll leave it to the fleet list spreadsheeters to work out the exact proportions of full size vs smaller bus types, their date of entry into service and thus future dates for withdrawal and how well current orders match the steady state replacement profile.