In the UK there are currently around 3,200 road deaths annually, compared with more than 7,000 a year in the 1960s.
This improvement is due to a number of factors, including seatbelts, improved car design, the breathalyser and traffic-calming measures.
How do they know this?
Reducing the speed limit in towns might have repercussions outside of towns if drivers feel the need to save time by speeding up. (Bit of a shaky devils advocate attempt)
20mph seems too slow to me. I can see the benefits in a city centre, but on suburban roads and corridors into the city centre it seems too slow. Maybe I'm too used to 30mph.
Do those who advocate it drive at 20mph in a 30mph limit normally?
Are most accidents on the roads caused by people driving inside the speed limit?
I tend to think it's the culture that needs to change rather than the limit.