The blue car will drive through the intersection:

Erklärung

A vehicle displaying a qualifying special beacon together with the special audible signal must be let through before ordinary traffic. With no signs, signals, or markings controlling the remaining drivers, they then give way to traffic approaching from their right, so the green car crosses before the blue and red cars. The blue car is directly behind the red car and travels with it only after those two movements; placing the pair earlier would take them ahead of either the special-signal vehicle or the vehicle on their right.