Or even speed. What's the average speed of a tractor in exercise ? 15 mph ?[1] anticipation need, which was already pretty low in a field, gets even closer to zero.
So I fail to see what Deere did. A 10mph, pretty stable, on mostly flat (curved, but locally flat) land, with almost nothing of its size to interfere (won't a beef move away if a tractor aims at him ?), except avoiding the occasional tree .. I fail to see what problem they had.
[1] quick googling says some countries impose speed limit of 20mph but I don't know if it's on public roads and not private land. http://www.fwi.co.uk/machinery/road-rules-for-tractors-in-th...