How did things get transported? Mostly by horse and carriage? Even in WW2, horses and carriages were used quite a lot by the Wehrmacht. Also, it seems that very few Uberlandwagens were even constructed by the German after all.
That's an easy one - the primary transport of materials over long distances was done by rail. The existing railway network in North-Eastern France was quite dense before WW1 and this was enhanced during the war. Close to the front there was a network of narrow gauge railways although the Allies seem to have been bigger users of this than the Germans.
Road transport, whether by trucks or horses, was the last mile (or so) of transport. I gather the French evolved practice of moving heavy field artillery considerable distances by road (the RALTs) in 1917-18 was considered quite revolutionary.
Arguably the Western Front would probably not have settled down to a static war of attrition if it hadn't been for the railway networks. On the Eastern Front the railway networks were much sparser and the conflict didn't turn into a war of attrition.
