From the front of Porta Nuova railway station, look across the street toward Piazza Carlo Felice (large public square/garden in front of the station). The bus stop is on the right-hand of the square if facing it from the station, along the main street. Look for the standard Arriva bus stop sign.
The boarding point is located just outside the exit of the Arrivals level (ground floor). From the main Arrivals hall, look for the main exit doors leading outside. The bus stops/bays are situated right in front of this exit. Look for the standard Arriva bus stop sign.
