4 kilometers per hour.

according to the inquiry of the public network, in one section of National Highway 22, the sign with speed limit of 3 is less than 1 meters away from the sign with speed limit of 1. In Jianglou block of Huimin county, there is a sign with a speed limit of 4 kilometers at 145 kilometers of National Highway 22. This sign and speed monitoring are set on the same suspension frame.

the speed limits of national highways are 8km, 6km and 4km per hour, which are mainly limited by different sections. The speed limits of national highways are 8 km/h, 6 km/h and 4 km/h, which are mainly limited by different sections.