The Washington State Patrol pilot flying overhead, radioed he had two readings of 75 mph on a black sedan traveling southbound on the freeway in a posted 60 mph zone. Upon the direction of the pilot I entered the freeway as the car passed over the overpass I had been parked below. I headed up the on-ramp and set my speed at 70 mph to see if the black sedan would be pulling away from me. As I pulled in behind and in the lane next to this black Lincoln sedan, the pilot radioed, I w have the car at 80 mph . I increased my speed to 80 mph as the pilot radioed again, The car is w doing 90 mph . I ticed the Lincoln was still pulling away from me so I continued to increase my speed. The pilot radioed, The black sedan is w at 105 mph . I have had eugh; I sped up to 120 mph to get in behind the Lincoln to end this. The driver ticed my red lights, pulled over and stopped.