“If needing to replace vehicles just simply go to the depot and buy some new ones and sell of some old ones”
Correct. That sounds simple. Currenr status of the Train Fever allow that, just by few clics. But it cause huge economy drops. In numbers, on my las test I replaced aboout 100 horses for first lorry. It cost me about 1M. Cars go to the depot immeditaly so their load is wasted. Therfore I have sufferd about 3M losse in next two yars.
Theoreticaly, you could chcek if they have load, en then send to depo and then buy a new picece. Pretty fun to wath if you have 5 cars. If you have 100 its pain in the a.. .