Teller of untruths about one method of travel (4)
I believe the answer is:
liar
'teller of untruths' is the definition.
(I've seen this before)
'about one method of travel' is the wordplay.
'about' is a reversal indicator.
'one method of travel' becomes 'rail'.
'rail' written backwards gives 'LIAR'.
(Other definitions for liar that I've seen before include "Worse than a thief" , "Story teller?" , "man of fiction?" , "27 [DECEIVER]" , "one trying to sell pork pies" .)