forward-facing red lights indicate an emergency vehicle: police, fire or emergency medical services such as ambulances. Red usually means stop—think of stop signs and, of course, tail lights.

Two zones with three traffic lights, each already in use, are located on the outskirts of the city. A Ford Kuga Plugin Hybrid was used, conducting the test as if it were an emergency vehicle.

It used to be that a vehicle's gauge cluster lit up only when the driving lights themselves were on. Today, most clusters look the same whether the exterior lights are on or off. To know if your ...