And neither is possession of alcohol a crime. When you do something with alcohol that causes an increased risk of harm to others, like drinking and driving, the state can legitimately criminalize that conduct, much like might criminalize, say, indiscriminately discharging a firearm into the air.
That's all well and good about what you have to report, but the fact is that speed limits exist to ensure the safety of motorists, and, in many instances, pedestrians. If people drive faster, there is an increased risk of serious accidents. I don't want someone driving down my residential street at 75 miles an hour the same way I don't want someone who just drank 12 beers to be coming towards me on a two-lane highway.
Unless a motorist is committing some kind of other offense, there is no way for this "increased risk" to be ascertained by a police officer without engaging in the kind of "random search" process that is clearly a violation of the Fourth Amendment.
Hmm. So if a policeman is driving along and sees a car swerving down the road, crossing the center line and otherwise failing to maintain control of his vehicle, you think the policeman's observation of the motorist's behavior is a "clear violation of the Fourth Amendment?"
Upon reflection, I realize that you might say that crossing the center line is, in itself, another violation. So throw that example out. Let's say a drunk driver passes out at a red light. A policeman, who is behind the driver, gets out to see why the motorist didn't proceed through the green light. The policeman looks in the window and sees the motorist passed out. Fourth Amendment violation?
There is already a motor vehicle violation that applies to situations like this . . . it's called reckless driving, and it's far more serious than simply "speeding."
I plan and design transportation systems for a living (including highways), and I can assure you that there is no truly legitimate legal basis for a jurisdiction to impose a statutory speed limit of 55 or 65 miles per hour on a highway that has been designed to safely accommodate vehicles moving at 75-85 miles per hour (under wet conditions, mind you). Sure -- a vehicle that travels at 85 miles per hour is more "dangerous" by any objective measure than one traveling at 65. But a vehicle traveling at 65 is more dangerous than one traveling at 45, 35, etc. For that matter, a vehicle traveling at 5 miles per hour represents an infinitely greater threat to public safety than one that is stationary. So let's just outlaw motor vehicles altogether, eh?
Which is your MADD chapter?