To come across something is to find it by chance without looking. You were not searching, and there it was.
The accident is the whole point, since something you were hunting for is not come across. It takes a direct object after across. There is a second and very common sense about impression, since somebody who comes across well in an interview seems good to other people, and coming across as arrogant is a warning about how you are read rather than how you are. Stumble upon is the informal equivalent of the first sense.
1phrasecome acrossTo find something by chance.
“You may come across the receipt when you clear the drawer.”
2phrasegiveTo give a particular impression to others.
“He does come across as rather cold at first.”
Also accepted in games: stumble upon
Practised in Phrasal Verbs, A Man Called Ove
First appears in chapter 31 of A Man Called Ove.
Practise this word