Stoplights.
A flashing amber light means approach the lock at a safe speed and under full control.
"How many stoplights are on Main Street, if you know?"
If they have a green flashing light on top of their car, then they are a Doctor, and have as much priority as a regular emergency vehicle.
1/2*1/2*1/2*1/2*1/2=1/32
Cleared to cross
Green
Green
unknown
In Ontario, green flashing lights are used by Volunteer Fire Fighters responding to a call. Please pull over to let them by.
green lights keep flashing everything in the fridge froze yesterday
doctor on an emergency call