Meleches Uman, skilled labor, is not permitted on Chol Hamo'ed even for the needs of the mo'ed (M.B. 540:1).
Common practice indicates that driving on Chol Hamo'ed is allowed. However, driving is a melacha (burning) and it seems to be a skilled activity, as it takes practice to learn how to do it. So why is it allowed on Chol Hamo'ed?
I have a theory as to why it is accepted as being permitted, but I am looking for a source that discusses and permits this explicitly.