The Metro of Porto Line C (Linha da Maia) affords an option to walking the most durable part of the camino leaving Porto.
The split between the Central and Braga routes occurs at the Chapel of the Ramada Alta, a small church roughly 1.5km from where the pedestrian zone ended. Walk around the church, keeping it on your left, and follow the road behind the church. At the fork, turn right. Street signs indicate that you have left Largo Ramada Alta and are now on Rua de Nove de Julio.
The road ends at apartments, which you pass under. Cross the road and cross under the apartments opposite as well. Where you emerge from the second set of apartments, turn left.
This road (still the Nove de Julio) merges with another. Keep going straight. Eventually, you will pass under the highway. From here there is nothing to do but keep on going straight. You will eventually pass under another highway, where the camino splits into two distinct options.