Turning to the great Grand-Daddy Railroad of them all, let's look at DragonLance DL-1, Dragons of Despair.
Macro acceptable railroad. There is an adventure where you are going to escape capture in the Inn of the Last Home and ultimately rescue this barbarian princess and her magic staff from capture and find out where it came from and what it means.
This is acceptable railroading on a macro scale.
The module progresses to more heavy-handed tactics. As the armies advance, they tightens the noose across the lands of Ansalon, forcing all player movement to a choke point at Xak Tsaroth - where the "dungeon" is.
This is heavy-handed, but might be objectionable to some players and 'okay" to others.
Lastly, there is an encounter with the elves where they take you prisoner and forcibly bring you to the Forest Master - an encounter which is, in turn, a one way trip via pegasi to the swamps of Xak Tsaroth.