In the president's motorcade, a vehicle carrying photographers collided with an ambulance as it traveled to the event, and was struck by a falling tree limb as it returned.

VOA: standard.2010.02.06

In the case of the ambulance and police car, it's more a question of brightness.

警车和救护车上之所以用红灯，大多是因为红灯亮度大。

耶鲁公开课 - 文学理论导论课程节选

John Demjanjuk arrived at the Munich courthouse in an ambulance.

VOA: standard.2009.11.30