I have been involved in emergency services for many years mostly in EMS and fire but have since had to give it up recently due to medical reasons.
The actual law states that the police only need the a red light flashing to exceed the speed limit and bypass traffic but take my word for it, its not as glamorous as it seems...yeah the first 6 months or so its pretty cool but after that you realize how truly dangerous it is and you just want to get there as fast as you can and safe as you can so you can get home to your girlfriend, wife, kids, xbox, etc...
As far as turning the siren off after the lights yeah, most cops like to sneak up and catch the guy in the act and intersections are the most dangerous areas hence the need for the quick warning. Also we also get canceled or downgraded all the time.
Granted there is always some bad apples that give a bad name, but its a tough job you get criticized for not responding fast enough and then for driving to fast...give these guys a break already
Speedy
1985 300ZX & 1991 300ZX