Driving marked and unmarked cars. They some time part behind the bridge at exit 22. They use a white unmarked car with out blue or red light on top and sometime with out and blue light. The other day a policeman in unmarked car check lady at 85 in 70 MPH zone on I-65N. Gave chase and tried stopping her car by bumping her back bumper several time. She speed up to over 100 MPH. THP was called and gave chase at a distance and then the THP dispatcher called the chase off as he had the license number and unstolen. At Cool Springs area above Franklin, TN the THP finally stopped the lady. She said that she did not know who the policeman was as plain car with tinted windows.