The English language has no universal rule for when to double a consonant before the suffix "-ing".

As evidence that there is no universal rule, consider the word "travel." It ends consonant-vowel-consonant, but both the forms "travelling" and "traveling" are widely used. Writers of US English usually write "traveling" (but sometimes write "travelling"), while other writers usually write "travelling" (but sometimes write "traveling").

In short, there are educated, literate, native English speakers using the spelling "traveling" as well as the spelling "travelling"; which spelling they use is correlated with (but not completely determined by) whether they are considered "American English" writers.

The word "happen" also ends consonant-vowel-consonant, but almost everybody writes "happening" rather than "happenning", "editing" rather than "editting", and "orbiting" rather than "orbitting".

The explanation I recall from grade school for why we double the final consonant of certain words when adding certain suffixes (such as "-ed" or "-ing") because to add the suffix without doubling the final consonant would cause the preceding vowel to change from a short vowel to a long vowel.

Compare the "silent E" rule that explains the difference in pronunciation between "cap" and "cape", between "kit" and "kite", or between "not" and "note", and observe what happens when a "silent E" word takes the suffix "-ing": the final "silent E" is deleted and "-ing" substituted in its place, for example, "to bite" becomes "biting".

In fact:

• "siting" is a form of the verb "to site";
• "planing" is a form of the verb "to plane;" and
• "stoping" is a form of the verb "to stope".

I never knew "stope" was a word until I researched this question, but I was fairly sure that if it were a word, it would rhyme with "hope" (which it does), and that "stoping" would be pronounced differently from "stopping." That is how strong the "silent E" rule is in English.

The "silent E" rule and the rules for doubling the final consonant after a short vowel are weakened when the final syllable is not stressed. For example, "approximate" can rhyme with "mate" or be a near-rhyme with "mitt", depending on whether it is a verb or an adjective (at least in US English). Likewise, we have already seen the lack of a doubled consonant before "-ing" in "happening", "editing", and "orbiting". And of course even with stressed syllables there are pesky exceptions, such as "living" and "giving" (forms of the verbs "live" and "give", which also break the "silent E" rule).