There can be "voids" in the roads where the road crosses a terrain tile edge or if the same type of road crosses each other.
If you are talking about the road's termination or Last Point, they are different for each type of track. Train Tracks stop in keypad 9 of the tile, Roads in keypad 7, and Rivers in keypad 1. So for factories using Train Tracks, the tracks would have to come from the south or west to pass close to a factory that is sitting on keypad 5. Tracks will place a "station" object at the end of the Train Tracks and Roads – and possibly Rivers too. Are these objects visible?
If you are talking about the road's not crossing into the factory's tile try setting the factory's terrain sub-tiles to zeros (0s) and see if that changes anything.
Is the factory placed on the edge of the terrain tile, above the terrain elevation, or on top of the tracks?