I can't remember exactly which but a country in Scandinavia cut traffic deaths huge just by reducing the in town speeds to 40kph and then enforced it.
Should we be more worried about saving time than lives??
It isn't quite that simple. Here's a completely random google streetview from the residential area of a town in Sweden. Street View · Google Maps
If you go to the map view, you'll note that this is a dead-end neighborhood unless you're walking or on a bicycle, and that's an offshoot from another street that doesn't really go anywhere, either, and if you try hard enough heading northbound, you eventually get to the junction of a main road, which looks like this:
Note the dual carriageway layout with completely separate bicycle / pedestrian paths ... and the bicycle paths that go off yonder directly into a park area alongside a river that you can't easily get to with a car.
The roads layout - for the most part - doesn't facilitate people driving through residential neighborhoods unless home or destination is actually in that neighborhood, and it isn't a straight path to get there, and the layout doesn't facilitate driving fast. And the main roads, for the most part, have bicyclists and pedestrians physically separated from motor vehicles.
It isn't all like this, but a lot of it is. Many of these towns (not the area shown above) pre-date motor vehicles, and those also tend to be tight, narrow, and without many straight paths from one place to another.
Random German village (beautiful) - Tight, narrow. Street View · Google Maps