Driving south on I-45 between mileage marker 269-273 is obviously a designed speed trap. This is a multilane Interstate highway that has an unrealistic speed of 60 MPH. This is in contrast to basic 65 night 70 day. Police are in left lane under the bridge with lights off. They shot into southbound traffic and I was at best going 65. I was told that I was clocked at 79 MPH which was a lie. He apparently got some spurious target. I only observed him about 20 ft from his position. This was on a Friday night around 6 PM. This morning Monday at the same location 273-269 northbound I-45 at 0500 AM Dallas Sheriff Patrols were again working the area. I am certain that there are areas of Dallas County that are going without surveillence due to lack of manpower due to this activity.