Slightly adapting the first definition of the single noun room in Merriam-Webster's Eleventh Collegiate Dictionary (2003) yields this definition of room ahead:
an extent of space [in front of one] ... sufficient or available for something.
For example, you might say, "I think there is room ahead for my car to pass the slow car in front of me before any oncoming vehicles appear."
Headroom, meanwhile, has its own entry in the dictionary:
vertical space in which to to stand, sit, or move
For example, you might say, "This compact car has so little headroom that my hair brushes the ceiling every time I turn my head."
(This is essentially a restatement of Josh61's comment from two months ago.)