It is actually pretty simple..
On creation of the object - give it an instance variable from 1 to 5 to decide on which lane it is
Give the player an instance variable to decide on which lane He is..
For each object
-- system compare player.lane<object.lane
object send to top of layer
-- else
-- object send to bottom of layer
player on collision with object
system compare player.lane=object.lane
player die horribly
or if you want to only set it on collision
player on collision with object
---system compare player.lane=object.lane
player die horribly
--- else
---system compare player.lane<object.lane
object send to top of layer
--- else
object send to bottom of layer