To answer the question asked. I have pulled someone over before doing exactly what Malve described.
For the other questions that are out there, yes, a police officer driving does indeed have to obey the traffic laws, unless circumstances dictate otherwise. For example, emergency call, or during other course of their required duty. Every state and many jurisdictions have varying rules regarding this. In Oregon, a police vehicle can violate traffic code if responding to a call for service, positioning or attempting to apprehend a violator where the apprehension could be hindered by the use of lights and/or siren. So, sitting in a No Parking zone waiting for someone to run a red light is permissible. As is speeding to catch a speeder.
Here's a scenario to consider. This is what happened on one of the times I did what Malve is suggesting:
I was on I-5 southbound coming out of down town Portland when I saw a vehicle get on from the Hood Avenue on ramp at a higher rate of speed than traffic. I accelerated to get close enough to do a good pace(*) when I noticed in my rear view mirror a VW changing lanes coming up behind me at an even higher rate of speed. While I was originally pacing the Acura that got on the highway, I continued south and accelerated to 80 (I estimated the Acura was going 75 in a 55). At 80, the VW was still approaching, so I went to 85. The VW continued to approach until it was about 10 lengths behind me where it slowed to match my speed.
I pulled into the right lane, it eventually passed me, and I pulled it over for 85/55.
*pace - Some people think an officer has to "pace" someone for a set distance. This isn't the case (at least in Oregon). If I am going a set speed and I can see a visual disparity between my speed and the other vehicle's speed (ie: it's visually pulling away from me), that's all that's needed to establish that the vehicle is going at least as fast as I was.
Same is true with radar. If I see a big truck and a car coming towards me, and I use a radar and get a reading of say 80, but I can clearly see that the car is going faster than the truck, I can write the car a ticket for 80 because I can articulate that he was going at least 80. In other words, if my radar got the truck, and I can see the car is passing the truck, I can clearly and conclusively prove the car was going at least 80.
