The truth about Portsmouth

Some press reports claim that introducing 20 mph limits results in more collisions and injuries. This is wrong. The Department for Transport and organisations representing cyclists, pedestrians and children are all calling for 20 mph limits to be introduced on residential streets because slower traffic speeds make our roads safer. At 20 mph a driver has more time to react if someone makes a mistake, and can stop in almost half the distance compared to 30 mph. If a pedestrian is hit at 30 mph they are seven times more likely to be killed than at 20 mph.

So why are the press reports misleading? Here’s a few examples:

The Portsmouth 20 mph scheme led to an increase in KSI (Killed and seriously injured) – MISLEADING

In 2010 press reports highlighted an increase in KSI following the introduction of 20 mph limits in Portsmouth. This was based on a report published by the Department for Transport examining the scheme. The report looked at all injuries: deaths, serious injuries and slight injuries on the streets included in the scheme. In total there was an average of 182 injury collisions per year before the scheme and 142 per year afterwards. The report concluded that “early figures suggest that the implementation of the 20 mph Speed Limit scheme has been associated with reductions in road casualty numbers.” However the average figures for deaths and serious injuries (KSI) went up from 18.7 per year to 19.9, and the press chose to highlight this. KSI figures for one town or city tend to be small and fluctuate substantially from year to year so this slight rise . As the report noted, “the total numbers of KSI accidents are small across all sectors and are therefore susceptible to variations.”
For more see:…
Original DfT report:…

Casualties in Portsmouth went up in 2011 – MISLEADING

In July 2012, a press release by the Association of British Drivers highlighted a 57% increase in deaths and serious injuries (KSI) in Portsmouth in 2011 and again drew the conclusion that 20 mph limits were not working. This was picked up by many national newspapers. Again this was misleading. While there had been a significant increase in overall casualties in Portsmouth, the reality was that the vast majority of the increase was on roads with 30 mph and higher speed limits. On 20 mph roads there had only been a small increase with just four more KSI than the previous year. It was notable that there had also been increases in KSI across the whole of Hampshire between 2010 and 2011. For more see:

Casualties have gone up on 20 mph roads across the UK – MISLEADING

In August 2012, the Sun newspaper, the BBC and others all reported that the number of casualties had gone up 24% on 20 mph roads in 2011 compared to 2010. While this was true, the most likely reason was that there had been a dramatic increase in the number of roads with 20 mph limits. Towns and cities across the UK had started reducing the speed limits on thousands of residential streets from 30 mph to 20 mph to improve safety. The evidence is clear that slower speeds result in fewer collisions. For more see:…

For a summary of the effect of 20 mph limits on the numbers of casualties in the areas where they have been introduced, please see this table produced by RoadSafety GB.

It is important to note that, as with drink driving, it may take many years for some drivers to change their attitudes to speed in residential roads. However the evidence is clear, 20 mph is the right speed limit where people and traffic mix.