I have noticed that in the verb "to travel " , we have the choice to either say ' travelled" (British) or Traveled (US) , but when it comes to the verb to control , we can only use , controlled or controlling , so wanted to know if there is a rule so we can distinguish the verbs that take two L , or we have the choice to either double the l or leave it solo
I imagine that American English follows the standard rule of normally doubling the final single consonant after a single vowel letter in a stressed syllable:
counter - countered
refer - referred
travel - traveled
control - controlled.
We do this in British English with a few exceptions - one of which is that we always double final '-l' even if the syllable is not stressed.