IT is a striking claim: reducing the speed limit in all built-up areas to 20mph could save the public in Scotland up to £39.9million a year. But here’s an even more striking claim: it would also prevent five road deaths a year and reduce casualties by 755. If true, those kind of figures are hard to argue with. Why on earth would we allow people to drive at 30mph if five lives can be saved every year?

Of course, some caution is always needed with any projections of this kind – predicting the savings from policy changes is notoriously hard to do. We should also be careful about any kind of one-size-fits-all solution such as a blanket 20mph limit in all built-up areas – there are many roads in cities and towns where 30mph may be perfectly suitable. And there’s another important question: will there be sufficient resources to police any such change?

However, the figures from the Glasgow Centre for Population Health have not been plucked from the air – they are based on some solid evidence. A 20mph limit was introduced across Edinburgh in 2016 and the evidence is that the number of people being killed or seriously injured has fallen by almost a third.

There are other convincing reasons for supporting a reduction in the speed limit. Driving at a lower speed is more fuel-efficient which should mean less pollution. The statistics for accidents at 20 and 30mph are also striking: a pedestrian is seven times less likely to die if hit at 20mph than 30mph. And there is evidence that driving at a slower, more constant speed leads to less congestion on the roads, which is often caused by drivers repeatedly speeding up and braking. Every driver should welcome that prospect: fewer traffic jams.

The truth is that no one quite knows how a national 20mph default limit would work, but there is certainly enough evidence to support taking the idea forward. The Green MSP Mark Ruskell has been progressing his Proposed Restricted Roads (20mph Limit) (Scotland) Bill through the Scottish Parliament and the Government should approach the bill with an open mind. A national trial, with a subsequent review after a year, is certainly justified – for the sake of those potential millions saved for the public purse, but especially for the sake of those potential saved lives.