Costanera Norte is an urban highway that extends from east to west of Santiago de Chile, connecting the upper sector of the city with the airport and with route 68 that links it to Valparaíso, Viña del Mar and other towns on the central coast. It is currently considered, both for its technology and its benefits, one of the most modern urban motorways in the world. The public address and voice alarm system of the tunnels of the highway has been made with the COMPACT system, with a digital audio matrix in each of the four electric control rooms, capacity to control up to 62 speaker zones from the remote microphone desk and more than 8,000 W of power. The announcements in the tunnels are transmitted via horn speakers made in aluminium and steel, the AC-650T, with an RMS power of 50 W in 100 V line, maximum sound pressure level of 133 dB and an adequate frequency response for guarantee the needed intelligibility in such adverse environment as a road tunnel.