Changes

Second opinion : you can walk to the entrance of the "périphérique" (ring road) at Pont Jumeaux as well (10mns walk from metro Canal du Midi), there are 2 traffic lights there. Easy to go there (plus standing at the péage might be forbidden), nice spot, but took me like 1 hour to get a ride, both times.

Take metro line B in the direction ''Ramonville'' to the very last stop. After exiting the station, cross the street at the intersection and turn left (failing to cross the street will result in having to backtrack). Follow the autoroute signs (don't turn after he bridge about 1km walk) to the entrance of the highway you should find cardboard there, the peage is 2km after.