Hi Andreas,
First question to answer is what type of peat you're transporting:
If it's the milled peat like that transported in contemporary Bord na Mona trains for use as fuel in power plants (or in the manufacture of briquettes and peat moss fertiliser), then it will be powdery - almost sand like.
If its the traditional sods of turf burnt in homes across Ireland and carried in the WW2 era turf trains to Dublin, then the sods will typically be rectangular/box shape about 10cm thick and 30 to 40cm long - this is what Broithe is describing above