On French highways recently, a sign that confuses many drivers has been appearing more frequently—a blue square with a white diamond in the center. Although it may seem unfamiliar at first glance, its role is very concrete, and it is important for drivers to understand it correctly, especially if traveling through France. This sign indicates a special traffic lane reserved for vehicles with multiple passengers, known as a "carpool" or HOV (High-Occupancy Vehicle) lane. Its purpose is to reduce congestion and lower harmful gas emissions, particularly near larger cities like Lyon, Grenoble, and Strasbourg. When the sign is active, only the following vehicles may use this lane: Driving in this lane without meeting the conditions can result in a fine of around 135 euros. French authorities use advanced cameras and sensors that can detect the number of passengers in a vehicle, making violations easy to identify. Therefore, it is important to pay attention to this sign and understand its meaning. Although it is not a matter of danger, ignorance of the rules can cost you dearly. If you plan to drive through France, it is recommended to familiarize yourself with local traffic regulations in advance to avoid unpleasant surprises on the road.