Really? I don't know of any major metro area where you can "walk safely", especially not after dark.
There are lots. Of course, a "major metro area" has a LOT of component areas. Some are safe, high priced havens, while other component areas are complete and total crime ridden *expletive deleted*it holes.
For example, Philadelphia. But wait, that's a crime ridden *expletive deleted*it hole of monumental proportions, right?
Again, it depends on WHERE in Philadelphia.
Nicetown (actually Tioga and Nicetown) in North Philly. You don't want to be there at any time of the freaking day OR night. Or ever.
The crime rate is over 2,600 per 100,000.
Safest neighborhoods, where it actually is safe and family oriented?
Try Chestnut Hill, Upper Roxborough or Rittenhouse Square.
Sure, there's crime there, too, but it's not bad for a major metropolitan area.
So yeah, you CAN walk safely in many major metropolitan areas, as long as you know where you are.