Actually he has, to escape the black flash (death) he runs the the end of the universe where death is no longer a relevant concept because nothing existed
And this is why The Flash is a stupid character. Can't move faster than the speed of light. It's physics. His mass would become infinite at that speed.
That's why the speed force was invented, that's why he has the infinite mass punch. He doesn't obey common physics, the speed force allows him to transcend it
Unless he gets tired, then he'd have to set up camp along the running thing