I took a trip out there one time and I saw the cops doing it. They would have a cop car in each lane doing 55. No way around, we all had to drive 55.
They did that one year to screw up the traffic heading to the beach via Beltway & Rt 50. I think it was a failure so badly they never tried it again.
Average speed of the Beltway is around 65 with some doing 80.