In fact, we actually have the proof that it's impossible : friend of mine who has a devkit look very deep in ODST datas and saw that there were effectively 10 districts in New Mombasa Streets (0 to 9), but 3 of them were just unaccessible through "New Mombasa Streets" mission.
So why are they still here, and why didn't they just "deleted" them ?
Maybe there is a way to find, but we're quite sure that they aren't "unlockable" during the game without some specific material, like Devkit or other.
But, we can say that, during Coastal Highway mission, district 01 is special : in fact, the invisible ceiling is very close to the ground, and the accessible streets are downer than the others in this district ; i don't know if you use that expression, but this is quite like a "basin" , and that's why we can't go on the blue barriers.
Tepec