.... must be police or a fire truck coming.
In the what-will-they-think-of-next department, a news release from Lt. Terry Hastings at the LRPD with announcement of a news conference:
Today the Little Rock Police Department and Little Rock Fire Department will demonstrate our new vehicle sirens. The new sirens have a feature that allows you to feel the sound of the siren as an emergency vehicle approaches. In today’s society sirens are a common thing and new vehicles are made more sound proof to cut out road noise. Many times this means the sirens on our emergency vehicles are not heard until the emergency vehicle is near. These new sirens will help reduce accidents and make drivers aware of an approaching emergency vehicle sooner and allow time for them to react quicker.