Without a doubt, vampires can run faster than any car on Earth. But still they use cars during emergency situations when comfort has a low priority. Why?
Out-of-universe, cars are easy, look good, require little to no post-production effects to pull off, and can pull off some cool moves in-frame. Cars also allow for relatively easy exposition or dialogue scenes as the actors don't have to mime running while not showing exertion and while having a normal-volume conversation.
In-universe, cars are less conspicuous than someone running at highway speeds, they can be used to transport humans in a slightly more protective shell than simply being carried (and so as a corollary look less ridiculous than an actor loaded down with more then one human), and they require less mental and physical exertion by the vampire; while a vampire CAN run, they may need some or all of their faculties for other things.