I just got to witness instant Karma

Awesome!!!

Love that you were able to see that he got stopped! I had a similar type situation years ago.

I was going home from work, a long 1 hour trip. The road had changed from the 4 lane divided highway to a single lane on each side with just a stripe in the middle. That road had a wide paved shoulder, not allowed to drive on it unless you were turning right and could get out of the way of the heavy traffic heading home.

I nearly jumped out of my skin when someone whizzed past going well past the speed limit ON the paved shoulder. You just don't expect to be passed on the shoulder.

I didn't get a half mile when guess what? Yep, a deputy had stopped him and was giving him a ticket. I know he got a ticket for speeding and I'm sure he wasn't allowed to be driving of the shoulder of the road. That is where people had to park their car temporarily if it broke down.

I could tell that I was NOT the only car yelling yes! and waving an arm in the air as we drove past!

That was instant. Love it.

The best answer ever to that "Where's a cop when you need him?" question! Awesome...

Oh the joy of seeing a jerk get his/her just desserts!

My guess is the cop thought they might be potentially drunk or high with the erratic driving.

Awesome!
Years ago, we lived on a fairly busy street near an intersection with a light. Once, I tried to pull out of my driveway to make a left toward the red light. Some woman in an SUV pulled up to close the gap and not let me into the line of cars, leaving me blocking the other lane. Karma! A police officer coming from the other direction pulled her over, let me into the line, and as I drove off I could hear him yelling at her about how rude and mean she was being when I was just trying to get out of the driveway.

Karma at its best. 

A similar thing happened to me some time ago. I was driving at the speed limit through one of the villages near me, a village that I used to live in at one time so I knew the problem with speeding cars. I had this jerk  so close to me that I thought he was sitting in my back seat. I was obviously not driving fast enough for him, never mind the speed limit. All of a sudden he pulled out and roared down the road. As I came round the next corner there was a police van with a speed camera parked on the grass verge. Yes,it flashed him so he would have had a £60 fine  through the post a few days later. It felt so satisfying.

My dad is a horrible tailgater. That, combined with the fact that DH and several friends have all been rear ended while stopped or nearly stopped, makes me a big-gap-leaver. I'm usually about half a car back, even when stopped, because I don't want to be pushed into the car in front of me.

I am however, mindful of making sure I'm not so far back that the car behind me can't clear the intersection. 

The ones who bug me are those who leave like 4 car lengths and then it clogs the intersection and the whole previous light, too.

Something similar happened to me once. I was in back to back traffic at a red light. The car behind me decided to take the shoulder to pass a bunch of people. Next thing you know, a cop flies by with his lights and siren blaring. When i got passed the light the cop was giving them a ticket. It made my day.

Ha! I would have yelled out my window "Thank you for your service!"

Same with me. I always leave room because it's just safer. I think people are assuming ill will when there is none. I leave space between me and other cars, there are often pedestrians crossing against the light when theyre not supposed to be. All of those things may make me pause, but it's not to screw over the person behind me.

I was the 151 like of your OP.

That may just be a record!

Yes it did. We were in another state for a wedding. I only had my bran new car for about 3 months! The guy who slammed into the back of us have no insurance or drivers license. The car was not even his. . BUT noone was hurt, he had a little girl in the front seat who was not wearing a seatbelt.