Changes

As hitching a ride standing on the road is quite difficult in Spain (especially in a big city like Madrid), it is probably better to follow these instructions:

Alternative1:

There is a small service station with a McDonalds in Pinto. Takethe Cercania C3 from Sol (or other stations from Central Madrid), should cost nearly 3 euros. Then get off at Pinto. Walk eastwards through several streets towards the motorway, via avenida isabel la catolica. Have a look at hitchwikimaps or googlemaps how to get there. It's around 1.5 km. Once in the service station, ask people. Apparently, there are a lot of people going through towards morocco, so you might get a long distance hitch towards south (although sometimes cars are packed). It might be better than alternative 2 which has little/local traffic