Cops driving through red lights?

Is this a normal thing? I'm pretty new to Houston so I'm not sure if this is normal behavior.

Last weekend by UH (wheeler & Spur 5) I was at a red light and watched a sheriff (it wasn't Harris county, but I didn't catch which county) come up behind me, go into the left turn lane and casually drive straight through the intersection. Then he did it again at the next intersection. The kicker is he then also drove right by a guy stopped changing a flat tire in the right lane on Spur 5 where it's 50mph.

My girlfriend was with me, and she told me a few weeks before, she was at a red light with her brother and an HPD car pulled up behind the car next to them and started laying on the horn at the guy in front of him. The guy freaked out and tried to pull over to let the cop pass, only to be hit by a car in the next lane. The cop just drove off.

In the 6 months or so that I've been here I've seen about half a dozen people just casually drive through red lights but wtf is with the cops doing this.