The London Assembly Transport Committee are considering an investigation into the costs and benefits of 20 mph zones after a recent bid for a borough-wide zone was rejected by the Mayor.
Lewisham Council agreed to implement a borough-wide zone earlier this year but have since had their bid rejected by Boris Johnson on 'money-saving grounds.'
Now that decision will be tested by the proposal for a thorough investigation into the zones.
According to a report sent to the London Assembly:
The likelihood of a pedestrian being killed when hit by a vehicle increases according to the speed of the vehicle. Research by the Department for Transport suggests that a pedestrian hit at 30mph has a 1 in 5 chance of dying; at 20mph the figure is 1 in 40.6
Reducing casualties also has the benefit of saving money. Estimates by the Department for Transport were that traffic incidents where a person was killed or seriously injured cost an average of £134,000. The average cost of a fatality is £1.19 million.
By contrast, it is estimated that the cost of setting up 'speed over time' cameras to police a borough-wide zone would be just £1 million.
The report also cites evidence that 20 mph zones improve the flow of traffic, which is purportedly one of Boris Johnson's main transport aims.
It also counters claims that the zones increase traffic speed elsewhere, and makes it clear that major thoroughfares would have to be excluded from the zones.
However, although 20 mph zones have been shown to significantly reduce casualties and costs, there is not thought to have been sufficient research into all of the effects of the establised 'blanket-zones.'
The proposed investigation would seek to fill in some of those gaps. The Transport Committee will discuss the proposal this Thursday.