They've started doing exactly that in a couple of the newer developments here in Gilroy (California). The roads within the development are significantly narrow

They've started doing exactly that in a couple of the newer developments here in Gilroy (California). The roads within the development are significantly narrower, but there are now bike lanes separated from the traffic by actual curbs instead of just a painted line, and the sidewalks are a bit wider, too. The biggest walkability boost is that all cul-de-sacs now have walkways at the top of the 'bubble', so that foot and bicycle traffic can pass straight on through. Also, roundabouts have replaced stoplights. On the more negative side, the other feature of these development is the size of the lots vs. the size of the homes on them. The houses are close enough that you could probably reach out a window and hand something to your neighbor without much effort, and while each house does have a (small) garage, there is very limited on-street parking. I have mixed feelings about whether it will succeed, simply because the locations chosen for these developments are many miles away from the nearest stores, so anyone who lives there is going to need to drive most of the time anyway. Some of this is just the chicken/egg problem, some of it unchangeable without completely flattening and rebuilding the city. It will be interesting to see how it goes. I personally am glad not to live in such a place, as it as cramped as any city dwelling, but without the positives that dense cities provide.