They still do not have to stay on the road, they can still go cross country anywhere they like.
If you where in control of a massive army, and you wanted to ambush your enemies stronghold, would you really move along the busiest roads to reach his stronghold to get spotted by them right away? No, you would flank the stronghold and at least slow their reaction time to your siege ambush.
Joseph B. Visscher - JBV3737
Bugs aren't the problem, figuring out how to fix them is.