It is correct to say "Drive safely" but many native English speakers say "Drive safe". It is grammatically incorrect, because "safe" is an adjective and should be used to describe or modify a noun (person, place or thing). The word "safely" is an adverb (most words that end in "ly" are adverbs). An adverb is used to describe or modify a verb. The word "drive" is a verb in the command (imperative) form. As you can see from the other answers, most people don't realize that they are saying this incorrectly. It is so common that it is acceptable as colloquial speech, but should not be used in formal writing.

Either is fine and correct to say. I think that technically "drive safely" is more grammatically correct, so if in an English exam put "drive safely". But in everyday speech you can use either phrase and it will have the exact same meaning and sentiment. I don't think one is more common than the other as I do use both, "drive safe" maybe a little more for informality and it's quickness as we do have a tendency to like to shorten words and sentences in English. Hope that helps.

It’s common for many short words (fast, smart, safe) to work both as adjectives and adverbs. For this particular use of ‘safe’, beware that it’s not grammatically approved, so don’t use it on a test. (Note, a different expression, ‘play it safe’, is perfectly fine. ) I say both.

Drive safely is more common here in England.

Drive safely is the correct answer