These photos illustrate why I usually take a train to the edge of the industrial belt area when walking from a major city (Lisbon, Porto, Madrid, Leon, Burgos, etc.) . The shoulder (or verge) in Portugal is a lot narrower than in Spain, in general.
When I walked from Lisbon in 2017, I found the first third of the distance to have too much road-walking for my personal preferences. Once I got to Tomar and Coimbra, things were a lot better. Then, as I approached Porto, this got increasingly grey (as in concrete). I adapted to this and overcame using a streetcar and bus to get in and the metro to get a lead start, skipping over the "blah" areas.
As I do not find walking through industrial areas to be conducive to thoughts, mediation, or safety, I avoid them when and where possible.
Just sayin...