A motor protein like kinesin-1 cannot use an IF as a track because it lacks polarity.
Can someone elaborate on this answer?
Polarity essentially means a plus end (growing/polymerising) and a minus end (depolymerising). Look at microtubule (MT) (http://en.wikipedia.org/wiki/Microtubule). So molecules such as Kinesin-1 (http://en.wikipedia.org/wiki/Kinesin) use the hetero-dimeric nature of MT (alpha and beta subunits) and its polarity to orient themselves and move directionally along MT in an energy dependent manner.