tame bone
Just give your objects a "speed" variable and multiply the velocity of the objects by it.
So when they step on the accelerating area, the area increases said variable.
Doing this with TileMaps is going to be considerably harder if you where using that. You would have to check for the tile coordinate of where the object is, then the TileData at that coordinate and maybe check its metadata to see if it has something like a "speed_increase" the object can use to accelerate itself.
prime notch