So, I've just completed all the levels except Downtown (and collected everything), but when I go to the Police Helipad in Cherry Tree Hills, I can't go to the Downtown section - even though I've built the Helipad there, and went from Downtown to Cherry Tree Hills that way. I thought that once you build a helipad, that unlocks that area so you can travel to it a lot easier.
If you haven't saved the fire station from the fire station maybe it won't let you. Maybe you have to finish more of the story
Yes - I've finished the whole game in Story Mode, and now I'm in free mode, going back and collecting everything else - cars, character tokens etc etc. I just can't work out why Downtown is always locked whenever I go to a helipad in any other area. :-/