How does a signposted 30 km/h zone (Tempo-30-Zone) apply to agricultural machinery?

1. It applies to passenger cars only; tractors may continue at 50 km/h
2. It sets a minimum speed, so a tractor must maintain 30 km/h
3. It applies only on school days and during school hours
4. It applies to every vehicle in the zone, so the tractor must not exceed 30 km/h anywhere within it