ŝoseo

One root, no seams. Ŝoseo will not divide. There is no ŝos- and no -eo suffix; the word came in whole from French chaussee and behaves like any other borrowed noun. The ŝ at the front is the French ch, which is the usual correspondence: ŝoforo, ŝanco, ŝoko.

What kind of road it is. Esperanto has a proper ladder here and it is worth learning as a set. A vojo is a way, any way, including the figurative one. A strato is a street, with buildings along it, in a town. A ŝoseo is the surfaced main road between places: the thing you leave town on. Above it sits the aŭtoŝoseo or aŭtovojo, the motorway with no crossings, and below it the vojeto, a lane or a path.

The gift in the etymology. A chaussee was originally a road built up with lime, calx, rammed into it: engineering, not surface dressing, which is why the word attached itself to the good roads rather than the tracks. English borrowed the same French word as causeway, kept it for the raised road across wet ground, and left the ordinary sense to the French. Esperanto took the ordinary sense.