Four new ambulances were placed into service this week by the city Emergency Medical Services Department.

The ambulances, which cost $190,000 each and have an additional $100,000 in equipment, are stationed at the Waianae, Nanakuli, Makakilo and Wahiawa stations.

The four 2013 Ford-350 ambulances are first to be equipped with siren called the howler — which emits a low frequency rumble — and works in addition to the siren to warn drivers.

The city maintains 20 ambulances and two rapid response vehicles, SUVs that don’t transport patients, but begin patient care or determine if the patient needs an ambulance.

All ambulance units are designated as advanced life support and are staffed by at least two people: emergency medical technicians trained in basic life support.; and mobile intensive care technicians trained and authorized to perform advanced life support and invasive medical techniques.