Formal or official term for an ambulance. In everyday conversation, 救急車 is overwhelmingly preferred.
See also: 救急車
I heard the siren of an ambulance.
The standard, everyday word for ambulance. 救急自動車 is a longer, more formal synonym rarely used in casual speech.
Compound of 救急 (emergency medical care) and 自動車 (automobile). A formal term likely coined in official or legal contexts.