What is the right behaviour now?

Your answer is correct because, according to German traffic rules, when a traffic light is red, you must remain stopped and keep your vehicle's engine turned off if you have chosen to stop for a longer duration, such as at a red light before it turns green. This helps to reduce emissions and save fuel.

The other options are incorrect because:

- Keeping the engine on until the lorry moves is not required and may waste fuel unnecessarily.
- Waiting to turn off the engine only when your light turns green is not correct, as you need to be ready to move as soon as the light changes and also minimize idling emissions during the stop.

In summary, it is best practice to switch off your engine once you have stopped at a red light, especially if you expect to wait for some time. This follows the German traffic guidelines aimed at environmental protection and fuel efficiency.