The turbo is NOT the same as your boost (A button). Turbo is a piece of equipment that you earn when you reach Level 9 racer in career mode.
This achievement requires that you fire off the turbo and have it burn out without hitting anything - not even signs or shortcut blockades!
Once you reach level 9 – head over to East Gorge Canyon (on the far right of the map – here you should find a new map called “Stampede” (hot pursuit). On this map the Turbo equipment is available. A good place to get this, is just after you leave the free way and enter the country/desert road. Here there is a long straight down hill where you can see oncoming traffic easy (just after you receive the warning about the Lamborghini cop being deployed).
Its easier to get this when you only have Turbo level 1 - since Lv1 Turbo lasts for a maximum of 10s, whereas a Lv3 Turbo can last up to 15s.
An easy trick, as stated by ivy0173, is to hit the brakes and gas at the same time and then fire off the turbo (up on the D pad). Keep holding the gas and breaks until the turbo is depleted. Beware that you will be moving some distance – so make sure you have clear road in front of you.