There are also "traffic calming" designs (some of which incorporate naked roads concepts) which can reduce accidents.

David Snowden (I ran across his name searching for items related to another Snowden in the news) mentions in a YouTube video a roundabout in England which, despite its visually frightening appearance and apparently very high traffic densities, is one of the safest intersections in the UK.

Traffic calming can be an issue though, because it reduces traffic speeds, which can actually increase overall risk when it slows down emergency vehicles. Especially in residential areas, you can end up reducing the number of minor traffic accidents at the expense of increasing the number of non-traffic-related fatalities by increasing the emergency response time of fire trucks and ambulances.

This is a non-problem:

1) The other road users are operating at a slower speed so it is considerably easier to get out of the way.

2) emergency access is affected by the issue causing the emergency ( a crash for example )

3) normal congestion will put the effective speed lower anyhow.

4) traffic calming can actually increase the throughput of a street For example, converting a street with 2 lanes each direction to a single lane with a central left turn lane: eliminates the congestion caused by people stopping to make turns from the left lane.

>The other road users are operating at a slower speed so it is considerably easier to get out of the way.

You're assuming the other traffic is the problem. Speed humps etc. will considerably slow down e.g. a fire truck even if there are zero other cars on the road.

>emergency access is affected by the issue causing the emergency ( a crash for example )

Again, you're assuming traffic to be the primary problem. If my house is on fire or there is some intruder then there will be negligible effect on the local traffic but structural impediments to haste will still delay the emergency response.

>normal congestion will put the effective speed lower anyhow.

Traffic again.

>traffic calming can actually increase the throughput of a street For example, converting a street with 2 lanes each direction to a single lane with a central left turn lane: eliminates the congestion caused by people stopping to make turns from the left lane.

That's not really traffic calming, or to the extent that it is, should be distinguished from what I'm complaining about, e.g. speed humps or other measures solely designed to reduce traffic speed or annoy motorists into being diverted onto other roads.

Also, the better solution in such cases is to make the road have 2 lanes in each direction and a central left turn lane.