Go to this part of the map and locate the jump onto the train tracks.
There's a glitch where the cops can't make the jump to follow you onto the train tracks. You can start a pursuit, jump on the tracks, and evade the pursuit by driving out of the pursuit radius.
You can also increase your heat level by parking on top of the tracks where you can still be seen. The cops can see you and continue to increase your heat, but they won't be able to bust you.
For The Heat is Off achievement, you need to escape at each individual heat level (one through six) and it will unlock. So start a pursuit at heat level 1 and jump on the tracks and escape. Start a new pursuit, get to heat 2, and escape. Repeat for heat 3-6.