I don't think it's so much that they don't want to bother unless you're close to 10 MPH over the limit, but that it's much harder to get a ticket for 3 MPH over the limit to stick in court.

It doesn't take much error or miscalibration in radar devices or a squad car's speedometer to explain "speeding" by 3-5 MPH to a judge; there's enough doubt about the absolute accuracy that such a defendant would likely get a case dismissed.

When you get to 10 MPH and up, though, that's a much harder point for the defendant to argue.

It's not unlike the way a fair number of DWI suspects who measure a .08 to .10 in their BAC tests wind up copping a plea for something less serious than DWI. There's enough reasonable doubt in measurements *that* close to the threshold that the DA would risk getting nothing at all, if the defense can convince the jury there's a reasonable chance that not everything about the measurement -- the method used, the time elapsed since the stop, the calibration of the equipment -- wasn't spot-on accurate.

Look. Everyone knows there's a cushion in Texas just like every other state. Yesterday I was doing 75 on a farm road and a cop passed me.

Just don't expect any police agency to actually admit to it. Because to do so would simply raise the speed limit up to the cushion and everone would then expect a new cushion on top of that. They're just not that stupid.

PS--

I drive I-35 quite a bit between Fort Worth and Austin. Well, actually as I live outside Waco I'm usually driving to either Fort Worth or Austin but not all the way between them at the same time.

Anyway, the two places where I almost always see speed traps from the local cops are just south of Waco in Lorena, especially at night, and just south of Fort Worth in Alvarado where I always see them. You can probably go 90 all the way between Austin and Fort Worth as long as you slow down in Lorena nad Alvarado. Those two cities must depend on I-35 speeders to fund their city budgets.