I remember my Visa runs to Vientiane I used to pass by an intersection with an arrow pointing towards Maha Sarakham. I could never imagine how the driver could remember the routes in the wee hours of the morning. Every damn road looks the same to me.
The only possibility of getting lost is after exiting from motorway 2 and entering the rural roads. This I admit lost many times.
The other road that connect to the remainjng one third of Issan is road 22, 23 and 24. These roads are much much more tricky as its not like motorway 2 that goes straight.
I am more confident of using motorway 2 than the Ubon bound roads 22-24. Lots of confusing road signs(hard to survive if cannot read Thai) and lots of border matas and soldiers road blocks.