I apologize, but I have to disagree on the facts. The lower route out of Villafranca del Bierzo is along the old highway, N-VI, and it has very little traffic, and is very quiet. It is painted yellow as in the Wizard of Oz! The yellow paint disappears a bit more each year. A major freeway, A-6, has replaced it, and you can see it at regular intervals, and hear it as well. However, there is less than one car per minute now using the old highway (both directions), and the barrier is a very solid Jersey wall. The path is on the left of the highway, but the small towns are on the right, so there is an occasional crossing for pilgrims, always marked with warning signs that exaggerate the actual hazard. The bars in the villages are on very quiet streets.
Trabadelo, where the high path rejoins, is across both a river and the old highway from the A-6. The route stays to the right of the river, but later crosses N-VI several times, with occasional shoulder walking. The marked path is not the shortest route in order to avoid shoulder walking. There is a truck stop/bus stop at Ambasmestas, so a lot of the A-6 traffic pulls off, crosses the N-VI, and into the restaurant. After Ambasmestas, there is only local traffic because the highway only goes to local places. It is road shoulder walking until Las Herrerias, an extremely quiet village before the ascent that goes eventually to O Cebreiro. You can see the A-6 overhead many times on the walk, and it has all the traffic except for local vehicles. Even that traffic disappears when you turn left to take the street to Las Herrerias. The N-VI wanders up some valleys to Piedrafita do Cebreiro (I walked it once). From Las Herrerias you will see only taxis heading for La Faba and O Cebreiro!
The vicinity of Ambasmestas has dangerous traffic, mostly from trucks. It is about four minutes of the walk. Except for the high ridge path, virtually everything is pavement. The river valley is narrow, so the river and N-VI use up most of the space. The A-6 is mostly on pylons because there was nothing at ground level to accommodate it.
It is a beautiful woodsy stretch of the camino along a fishable river. It is gently up (except for getting to the top of the ridge on the ridge route) until you start the climb to La Faba. I personally do not see anything there to avoid, but clearly opinions differ.
