FRSC, VEHICLE INSPECTION OFFICERS (VIO) AND POLICE (NPF). WHICH IS WHICH ?

I WAS IN A STATE OF DILEMA ON A FATEFUL DAY WHEN I DROVE OUT IN MY PRIVATE CAR. I GOT TO A CHECK POINT AND MET THESE DIFFERENT OFFICERS....FRSC OFFICERS, VEHICLE INSPECTION OFFICERS (VIO) AND POLICE (NPF). LO AND BEHOLD, EACH OF THESE DIFFERENT OFFICERS DEMANDED TO CHECK MY PARTICULARS AND DRIVER'S LICENCE.
HOUSE, I WAS CONFUSED EVEN TILL NOW.
PLEASE, WHO IS WHO AMONGST THESE UNIFORM MEN.
IT SEEMS THAT THEIR ROLES ARE NOT WELL DEFINED.
ABOVE ALL, I AM BRIBERY AVERSE!

JAYJAY