It depends on the route. When we evacuated for Hurricane Floyd, we took the so-called back road route. So did a jillion other evacuees. We sat for hours, not moving an inch, on a two-lane road in the woods, overnight.
Also, there are some routes that eventually, you're going to have to touch the interstate at some point.
A couple years, during another evacuation (we stayed at home), people couldn't even get out of downtown Charleston much less get on the interstate or back roads before they either ran out of time or gas. Charleston is built on a peninsula, so there are limited ways off of there.
A little tidbit of trivia for evacuees:
When traffic isn't moving, and you're stuck in the woods overnight, there will be buses escorted by police whizzing past you who are allowed to cut ahead. Those are the prisoners evacuated from the jails.
The buses that are stuck in traffic with the passengers duct taped into their seats are the elderly people evacuated from nursing homes.
There sometimes is no easy solution.