What does the speed limit of 30, 40, 50, 70 mean?

[JourneyRose]

According to Article 45 of the "Regulations for the Implementation of the Road Traffic Safety Law of the People's Republic of China": On roads without a central dividing line, the speed limit for urban roads is 30 kilometers per hour, and for highways, it is 40 kilometers per hour; on roads with only one motor vehicle lane in the same direction, the speed limit for urban roads is 50 kilometers per hour, and for highways, it is 70 kilometers per hour. The image shows a highway without a central dividing line, so the maximum speed limit is 40 kilometers per hour. Additional Information: Article 46: When a motor vehicle encounters any of the following situations, the maximum speed shall not exceed 30 kilometers per hour, and for tractors, battery-powered vehicles, and wheeled special-purpose motor vehicles, the speed shall not exceed 15 kilometers per hour: When entering or exiting a non-motorized vehicle lane, passing through a railway crossing, sharp curves, narrow roads, or narrow bridges; when making a U-turn, turning, or descending a steep slope; when encountering fog, rain, snow, dust, or hail with visibility less than 50 meters; when driving on icy, snowy, or muddy roads; when towing a malfunctioning motor vehicle.