Demanding one stops travelling by cab (7)
I believe the answer is:
taxiing
'travelling by cab' is the definition.
'taxiing' can be an answer for 'travelling' (taxiing is a kind of travelling). I am not certain of the 'by cab' bit.
'demanding one stops' is the wordplay.
'demanding' becomes 'taxing' (I've seen this before).
'one' becomes 'I' (Roman numeral).
'stops' indicates putting letters inside (to stop can mean to block a gap).
'taxing' enclosing 'i' is 'TAXIING'.
Can you help me to learn more?
(Other definitions for taxiing that I've seen before include "Starting or ending a flight" , "Running along the ground" .)