Walkable highways

It always kinds bothered me that I can neither walk nor bike on any major highway in my state. Aside from the obvious hazards of walking near speeding cars, what's the problem? Just make the walk/bike path farther away, or put up six foot guardrails.

Truth is, I secretly want to walk to DC this summer to demand the trial of GWB and co. for war crimes. I'll need a more direct path and easier press coverage. Use that new cool porous concrete or similar recycled material.