touge also tend to have much narrower roads, and less room for error. you can run smack into a mountain or rolling off the cliff. run off a gutter easier, etc.
realistically it takes even more skill because you have to watch out for the occasional upcoming traffic unlike on a circuit. and you dont usually have a co driver to do it like a rallyist. which is why real touge drivers rarely go full out unless it's a private touge track. but since this is a game, that would be unneccessary.
circuit tends to have a lot of grass and tires walls to decrease the impact.
if you build a circuit on a bumpy road with steep slopes, it'll have to be on a mountain pass which would be like a touge. and you'll still need to make the roads narrower(yes it's almost impossible to pass on some touge passes which is one of the reasons for the leader/follower rule).
if a touge pass was completely straight i guess that owuld be easier, but as it stands, thats rarely the case. circuites almost always have more long straightways and less consecutive hairpins followed by high speed corners. not to mention sometimes things like falling leaves which makes the road more slippery.
