MUNDANE MYSTERIES: Why Truckers Say “10-4”

Some truck driver slang just makes sense. Like “Bambi”, which means a deer is in the vicinity. “Go-go Juice” means diesel fuel. “Seat covers” are actually pants. But what about the phrase “10-4”. You may know that 10-4 basically means “okay” or “I got your message”, but why? Where did that come from?

10-4 came from what are called “ten-codes”, a group of digital short-codes developed in the late 1930s by Illinois State Police. After the recent invention of 2-way car radios, ten-codes were an easy & efficient way for police officers to transmit messages to & from each other & the police station. Then in 1940, APCO (the Association of Police Communications Officers) published a list of about 100 ten-codes as a way to standardize usage across state lines. 10-1 stood for “Receiving poorly,” 10-2 meant “Receiving well,” 10-3 was for “Stop transmitting,” while 10-4 meant “Acknowledgement”.

So, why did they tack a 10 onto the front of each number? It was a actually a troubleshooting tactic. Radio motor-generators weren’t high-tech enough at that time to jump into action as soon as someone started transmitting, so the person on the receiving end often didn’t hear the beginning of the message. But if the beginning of every message was the same meaningless 10, it didn’t matter.

Thanks to Broderick Crawford saying “10-4” on the 1950s police drama Highway Patrol, it gained traction with the general public. Then, when truck drivers started using via 2-way radios, they co-opted the ten-codes. Truckers’ radios were usually citizens band radios, or CB radios, which took off after the 1973 oil crisis, when 55-mph speed limits were instituted across the nation & truckers needed a way to warn each other about speed traps. Shortly thereafter, CB radio code talk took on a life of its own, thanks to C.W. McCall’s 1975 hit song “Convoy” and, later, the movie “Smokey & The Bandit”.

CB radios may not be as big of a thing nowadays, but 10-4 has never gone out of style as the go-to way to say “I Gotcha” (without actually saying “I Gotcha”).

Got a Mundane Mystery you’d like solved? Send me a message via Twitter (@AndyWebbRadio), or shoot me an email at [email protected].