Under national standard GB 1589-2016, what is the standard maximum vehicle height limit for standard commercial freight trucks, and what must a driver do when approaching an overhead height clearance sign (限高标志)?

1. Maximum height is 4.0 meters (4.2 meters for standard container chassis); drivers must confirm total loaded height is lower than the posted limit before entering
2. Maximum height is 4.5 meters; trucks may proceed through any underpass if traveling below 20 km/h
3. Maximum height is 3.5 meters; drivers must deflate suspension air springs prior to passing any overpass
4. Maximum height is unlimited on national highways; height restrictions only apply on residential city alleys