How is a lower speed limit than 50 km/h, such as a 30 km/h limit outside a school, legally established on a Chilean urban street?

1. The Ley de Tránsito itself fixes a nationwide 30 km/h limit for every school and hospital frontage
2. The municipality may raise or lower the statutory limit for a specific road, or declare a 'zona de tránsito calmado', and the change takes effect through official signage
3. Any driver may choose a lower limit and the police must accept it
4. Only the Dirección de Vialidad may change limits, and only on rural roads