For this reason, each guide device on the bidirectional guide system of the invention exists in two states: a director state when in the rigid configuration and a follower state when in the floating configuration; it adopts {HEAD ~ these states} alternately depending upon {TAIL ~ the vehicles direction} of travel 
depending upon
For this reason , each guide device on the bidirectional guide system of the invention exists in two states : a director state when in the rigid configuration and a follower state when in the floating configuration ; it adopts { HEAD ~ these states } alternately depending upon { TAIL ~ the vehicles direction } of travel
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH