A study had to be commissioned, after finding out that crows are social animals, near a busy highway.

Crows can recognise individual people, they post guard crows on buildings, light poles as they go down to find food.

Anyway, it seems they were ONLY getting killed by trucks on a busy highway, so cameras got installed and recordings were studied.

It turns out that the Guard crows can easily spot a hazard and screetch loudly "Cah!!! Cah!!!. But it seems they were completely unable to shout "Truck Truck".