Lee travelled to the Middle East during vacations.
Or had she traveled?
Travel, a simple and common word of English, when used in its derivative forms can be written in two ways; with a single l or with two ls. This can be seen in traveled and travelled, traveling and travelling and traveler. These variations in the spellings arose due to differences in American English and British English and often result in confusion among writers.
These differences are openly discussed in this article where origin, meanings, usage and examples are used to clear out these confusions.
The word travel originated from Middle English: a variant of travail, and originally in the same sense.
Travel as verb:
Travel is used as a verb in English language where it means to make a journey, typically of some length.
The vessel had been travelling from Libya to Ireland.
To journey along (a road) or through (a region) and to withstand a journey without illness or impairment is also called travel.
He usually travels well, but he did get a bit upset on a very rough crossing.
Travel is also used to describe the task of being successful away from the place of origin.
Accordion music travels well.
Travel is used to imply the meaning of (of an object or radiation) movement, typically in a constant or predictable way.
Light travels faster than sound.
Travel as verb:
The action of travelling is called travel as noun.
My job involves a lot of travel.
Something that is (of a device) sufficiently compact for use on a journey is called travel.
She packed a travel iron along with other things.
Travelling or traveling:
Travelling and traveling are the two spellings of the same word. Both of these spellings are acceptable and exchangeable in English language but their usage differ according to the part of the world they are spoken in. In American English, the inflected forms of travel take one l—so, traveled, traveling, traveler, etc. In varieties of English from outside the U.S., these forms take two l’s—travelled, travelling, traveller, etc.
On average, it traveled 4 to 5 miles an hour. [Los Angeles Times]
Morgan claimed the French vessel has been towing at 4 nautical miles, whereas the tugs could have traveled at 6 to 7 nautical miles. [Newsday (dead link)]
But perhaps the most logical of all explanations is that Romney is a time traveler. [Washington Post]
When to use which spellings?
If you reside in US, the acceptable spellings are the ones with a single l; traveling. However, if you belong to Europe, the acceptable spellings are with two ls; travelling. Remember to choose the spellings according to your audience too. If you are writing for American community, you should use American spellings and vice versa.