Answer:
Because the emergency vehicle has stopped ahead and it means that Move Over Law will be applicable.
Explanation:
The law which requires the motorists to give safety clearance to tow-truck drivers, fire-fighters ambulances by moving over and changing lanes. In US the drivers are required to give one lane buffer to the stopped emergency vehicles. these laws vary in across the states. So if you are moving in the right lane and encounter a stopped police car then the driver should move to one lane towards left to avoid any accidents.
