In Sliven Province the road crosses the easternmost reaches of the Sredna Gora mountain range and at the village of Asenovets descends to the Nova Zagora field, which is the northeasternmost part of the Upper Thracian Plain.

It crosses the western low areas of the Svetliyski Heights and passes through the villages of Radevo, Mlekarevo, Novoselets and Radetski and just north of the Maritsa Iztok-2 Thermal Power Plant the road reenters Stara Zagora Province.

[2] There, it passes through the dam of the Ovcharitsa Reservoir on the homonymous river, as well as through the villages of Polski Gradets, Madrets and Glavan,[2] after which it ascends the northern slopes of the small Sakar mountain range and enters Haskovo Province.

Between the villages of Cherepovo and Balgarska Polyana the road begins its descend through the southern slopes of Sakar along the valley of the Golyama reka, a left tributary of the Maritsa.

Threre, the II-55 passes though Pastrogor, forms a junction with the Maritsa motorway and in the center of the town of Svilengrad near the borders with Greece and Turkey it reaches its terminus at Km 370.7 of the first class I-8 road.