Changes

Get the metro to Pacci Pacii (note the metro is a bit crazy - if you're not careful the trains change lines without warning and you can end up at Gare Du Nord again!).

From Pacci Pacii find the main road going west, and go to the first bus stop. Get the first bus that says Carrefour and go all the way to Carrefour shopping centre, this is the start of the motorway. Theres a part where the fence is broken and you can access the motorway here - it's actually a very good spot to hitch, since traffic coming from the big shopping centre stops here.