Movies and Cops

So last night I went out to watch Sound Of My Voice which is a great movie. After I got done watching the movie I got onto the highway around 11pm at night. I was driving through a construction zone that had speed limit signs of 45. So I put it to 50 and cruise along. A van whizzes by me doing at least 65. I think to myself wow do they not realize the speed limit here? I mean there are orange barrels everywhere. I get close to my next exit, speed up to 55-60, and see in my mirror that the car that has been behind me for the past 2 miles is a cop. Moments after I had accelerated  the cop switched lanes and sped up to at least 70. I realized he had been following me and waiting for me to mess up. He had been there long enough to see the van go by me. Can anyone tell me what in the hell is wrong with that cop in letting someone go that was going 65 in a 45 and staying on my tail going 50 in 45? If anyone has a logical answer please let me know because I would love to know it. At least I had a great time watching Sound Of My Voice. If you like weird dramas about Cults that make you think twice about things, then give it a watch.

Trailer for Sound Of My Voice: