To lose the police you need to stay outside of their visual range long enough for your heat level to reset. It is simply a case of losing them, on the mini map you'll notice that while you're being pursued there is a visual range indicator;
Getting outside of that indicator will result in your heat level beginning to drop;
Once your heat level is below 5-6 bars you will enter initiate pursuit cooldown.
Once you're outside of the visual indicator and you've initiated pursuit cooldown, visiting a service station will reduce your heat level quicker as you pass through it. It will reduce your heat level once each time you go through it unless you've got 1 heat remaining, in which case it will immediately end the pursuit.
You can outrun them at low heat levels, but at higher heat levels you will need to utilise sharp corners, misdirection (ie: turning to go up an offramp or such like and then making a sudden turn that will send the police up the offramp while you drive on in a different direction) or causing accidents that block the road to give you some space.
You can also utilise the gameworld, by making jumps off ledges, smashing through billboards etc, which are routes that the police struggle to take properly. Another helpful trick is to turn your engine off while on cooldown. This greatly increases the rate at which your detection meter drops.