That was a bored or pissed off cop. That was surely thrown out in court. Speedometers aren't even that accurate.Years ago, an OHP Trooper was in a class with me, and he said that the secret about those fines being doubled in a construction zone was that only the fine itself (which is often a minimal part of the money paid) is doubled.
The bigger issue is that some DAs and municipal courts have figured out that they can tap that revenue stream just like law enforcement, so most of what you're paying isn't the actual fine, it's all the associated fees that get tacked onto it. There was a move to squash that in Oklahoma a few years ago, but I don't know what happened to it. It's probably like the move to squash civil forfeiture--deader than dirt. I know a friend of my dad's was up in arms because his grandson got a $200 ticket for going 1mph over the limit, but that was a few years ago.
As the old saying goes, don't steal--the government hates competition.