As a personal anecdote I can say that the last few times my home town have upgraded (or attempted to) their fleets of buses and light rail they have quite consi

As a personal anecdote I can say that the last few times my home town have upgraded (or attempted to) their fleets of buses and light rail they have quite consistently ended up buying vehicles that cant cope with the harsher winter conditions (I believe the manufacturers were in southern Europe in both cases) and break down. Add incompetence of local politicians and the far higher cost of renewing together and upgrading existing fleets is probably often a better move. Obviously it isn't an extreme long term solution though.