It says "Lane Change (In a Turn): +1 Dice."
We interpret that as you only roll the extra dice when you make the lane change.
Lol, kicks self and laughs it off
I was about to add a lengthy post regarding the interpretation of (In a 'Turn)' as you quoted from the player mats, and as I was writing it I realised that it is not reference the 'game turn' but the fact you are lane changing into a 'turn space', which makes perfect sense.
The way we had been playing it was if you make a lane change in your turn even if was in green, then when you enter a space where your speed requires a crash check an extra dice is added to the check. This was making changing lanes a bit more hazardous.