Impartial.. Not that i know any cops personally, and have only been stopped by traffic cops a few times. Once because i was driving very tired and someone reported me for drunk driving, apparently the police told the caller to follow me because i got the feeling the car behind was following me so i drove around the block and here and there to make shure. Yeop it was following me, the next thing i know its gone and there´s a copper behind me signalling to pull over

Anyway, they tested if was drunk and said "have a good day" and i pulled off into a parking lot and took a nap
The last itme i was out driving on a friday night, i was coming home at about 4AM or so and everyone got stopped and tested for drunk driving, as at that time people are comnign home from bars, the first comment i got when i rolled down the window was "pretty nice wheels"

We chatted a bit about my tyres wich are almost illegal due to wear, i brouht up the topic and they just said ill need to change before summer is over and wished me good day again
I have not met any nasty cops yet, and i dont honestly think there are that many. As long as you are friendly they dont have any reason to get nasty. If i would have said "Why the f*ck did you f*cking stop me for you f*cking f*ckers!?!" i think they might not have been as polite and i would probably have got a ticket for my tires..
Anyway, impartial.