What must you reckon with when you see this traffic sign?

This traffic sign is a German warning sign indicating possible traffic congestion ahead. According to German traffic rules, you must expect vehicles in front to suddenly brake or slow down due to the congestion. That is why the correct answers are that you should be prepared for traffic jams (congestion) and sudden braking by vehicles ahead.

It does not indicate that the roadway widens to three lanes, so that option is incorrect. The main goal of this sign is to alert drivers to be alert and ready to react to slow or stopped traffic, ensuring they maintain a safe following distance and drive cautiously to avoid collisions.