I am with Andrew on this. A motorized bicycle is still a must have, bug out device.
As we all know the most likely cause of a nuclear explosion, will of course be a containment and attempt to stop the zombie apocalypse. So there will be a short time and window of escape. In that and like BN said, the roads are just gonna clog and traffic will come to a stop.
So at the first signs of zombies, I will be bravely riding away