Liz, in some areas parents have started "walk-pools" to get their kids to/from school. Each parent has a day of the week to walk with all the kids from several families. That would be easy to organize if you can find just 4 other parents along the same route to school, and it would give your son the social experience of walking with other kids while minimizing the risk of getting run over. (That's a much bigger risk than abduction!) Over time, the kids will learn the skills they need to walk without an adult. You could assess your son's development of these skills by every so often asking him to narrate how he decides when to cross the street when you're walking together.
Naomi, I think you're right on target about teaching kids to take care of themselves while they're still kids. WickidaWitch's issues with her son are not really about street smarts, I think, but about his displaying generally poor judgment. For HER 14yo, allowing more independence at this stage would be a bad move, because he's shown he can't be trusted with what independence he has now. On average tho 14 is a good age to be learning to take care of yourself away from home.
My brother and I both did a lot of walking around as teens, in a pedestrian-unfriendly town, which in a different way is at least as dangerous as a city: Drivers aren't expecting to see pedestrians, and there are no sidewalks or crosswalks or 4-way stops. Often we had to be inventive to get where we were going. For instance, to get to the library, we walked thru residential sprawl for a mile, ran across the highway at a point 1/2 mile from the nearest stoplight, walked in 2-ft-high weeds along shoulder of Wal-Mart access road, ran down steep embankment into parking lot behind car dealership, crossed parking lot, wriggled thru gap in fence, jumped off 4-ft retaining wall into McDonald's parking lot, walked behind McD's and Long John Silver's, climbed down 60-degree-slope 12-ft-high concrete embankment to creek where it ran under other highway, crossed creek (only a few feet wide and deep) stepping on rocks, climbed up embankment on other side into woods full of poison ivy, came out of woods into K-mart lot, went into K-mart restrooms to wash off poison ivy, bought Icee, walked behind a dozen or so businesses while sharing Icee, took dirt trail thru unofficial trailer park behind Chinese restaurant (99% of the town had no idea anyone lived back there!), walked thru side-yard of nursing home, and emerged into library parking lot! Easy? No, but I've done it wearing a dress! without a net!
Fun? Well, more fun and more interesting than having parents drive us the two-and-a-half miles. Safe? Not perfectly, but we never got worse than a skinned knee, never encountered any unsavory characters, and reduced the risk of being hit by a car by staying away from the roads as much as possible. It was a great problem-solving and confidence-building exercise!