[7][8] The structuring axis is the Bordeaux–Sète line, which crosses the agglomeration in a north-west - south-east orientation,[7] following on a part of the route the Canal du Midi.

Then, a triangular junction allows to join the Brive-la-Gaillarde – Toulouse (via Capdenac) line, major axis of communication of the north-east of Midi-Pyrenees since it is from this that all tertiary lines stand out (Montauban–La Crémade, Tessonnières–Albi, Lexos–Montauban) sector, and which serves major cities such as Albi, Rodez, Castres or Mazamet.

Then, further north is the Montauban-Ville-Bourbon station from where the Orléans–Montauban line (or POLT, acronym for "Paris - Orléans - Limoges - Toulouse"), which is the old fast route that took the TEE Capitole and allows to reach the capital without passing through Bordeaux.

Then, they separate shortly after the twin tunnels of Guilhemery, half continuing south-east and, after crossing the small Montaudran station and several stations of the agglomeration (Labège-Innopole, Labège-Village, Escalquens, Montlaur, Baziège), continue towards Sète, Marseille or Spain via Perpignan; the other half goes southwest.

After crossing the Saint-Agne station, and its transfer with the line B of the metro, the line Toulouse - Bayonne crosses the Garonne and the Ramier Island, from which separate decommissioned tracks which allowed the origin to serve factories of the SNPE and those of AZF today destroyed following the disaster of the same name.

Then a second bifurcation takes place: This line is a kind of RER that joins the city of Colomiers to the west of Toulouse.