What does the road number 'S' stand for?

[SanJudah]

S stands for provincial road numbering. Brief introduction to the classification of domestic road numbering: The rules for domestic road numbering are primarily divided into three levels based on their administrative hierarchy: national highways and national trunk highways, provincial roads, and county roads. The initial letters of the Chinese pinyin for 'nation,' 'province,' and 'county'—G, S, and X—serve as their respective identifiers, with the identifier followed by numbers to form the numbering. Highway route numbers consist of a one-letter administrative level code and three digits. Differences in road signage: On road signs, those with a red background indicate national highways, while those with a yellow background indicate provincial roads. National highways refer to trunk roads with national political and economic significance, connecting major and medium-sized cities across the country and forming the framework of the national highway network. The numbering of national highways starts with the letter G.