I thought this was all a bit pie-in-the-sky, but on reflection if they closed off lots of roads to motor traffic lots more people would start using bikes or walking, and also lots more of people's needs would then become available at a local level, and this would be very good for community spirit and general wellbeing.
Sorry if I'm a zillion years behind everybody else in realising this, but I reckon we should close off more roads to bring about a much better way of living.
As Michael's helpful map shows us - many local roads do benefit from strategic closures that reduce or even stop through traffic:
The shaded areas are those that benefit from a strategic block. The ladder roads look like a strange anomaly in not having any protection.
It's true that if traffic levels are very low then it does become possible to have children cycling on the road safely. Unfortunately this is not the case with most of the closed off areas on the map - for example the Gardens has a constant stream of people parking, delivery vans (including those that deliver to Green Lanes shops & then go around gardens streets to turn around) etc.