What specific limitation does Article 27 of the Implementing Regulation impose on reversing a motor vehicle?

1. Reversing is allowed for any distance where hazard lights are on and the road behind is clear
2. Reversing is allowed only where necessary, must not exceed the length of the vehicle, and needs signals and a guide where required
3. Reversing is prohibited outright in car parks, service roads and residential streets
4. Reversing is allowed up to 500 metres against the flow of a one-way street to correct a missed exit