I imagine only someone in an area that may be totally blocked with traffic would need to consider this. If the streets are blocked a vehicle wont do any one much good. I have a bug out plan that revolves around my truck because I do not live in the city, and way...way down on my list I consider bugging out on foot in the unlikely event that the roads where I live become unusable somehow. Its more of a "just in case plan" because you never really can foresee ALL the things that could go wrong.

Plan for the worst and hope for the best.