I've had a road accident.
'Incidente' = een-chee-DEN-teh. Stress the second syllable of 'stradale': stra-DA-leh.
The first thing to say when calling 112/118 or flagging down a bystander after a collision.
'Ho avuto' is passato prossimo of 'avere un incidente', the standard fixed expression for having an accident. 'Stradale' specifies it is a road accident. In Italy you must call 112 or 118 immediately after any accident involving injury — failure to do so is a criminal offence under Article 189 of the Codice della Strada.
Sono stato/a coinvolto/a in un incidente.
I was involved in an accident.
More passive — use when you were not the driver at fault.
C'è stato uno scontro tra veicoli.
There has been a collision between vehicles.
Formal/official tone, suitable for police reports.
Mi hanno tamponato.
I've been rear-ended.
Tamponare = to rear-end; very common in Italian traffic vocabulary.
In Italy the 'Codice della Strada' (Highway Code, Legislative Decree 285/1992) requires all drivers involved in an accident with injuries to stop, provide assistance, and call emergency services. Leaving the scene (fuga) is a criminal offence.