Under the Road Traffic Safety Law of the PRC and national transport regulations, what is the maximum statutory speed limit for dangerous goods transport vehicles on expressways, and what is the speed limit under adverse weather conditions (fog, rain, snow with visibility under 50 meters)?

1. Maximum 80 km/h on expressways; maximum 30 km/h during adverse weather with low visibility
2. Maximum 120 km/h on expressways; maximum 80 km/h during adverse weather
3. Maximum 100 km/h on expressways; maximum 60 km/h during adverse weather
4. Maximum 60 km/h on expressways; maximum 5 km/h during adverse weather