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20mph Zones Increase Road Casualties

Published 04 July 2014

It’s official. In the week that a 20mph limit was imposed on the City of London, official figures prove that 20mph zones increase road casualties rather than reduce them.

Forget all the 20mph campaigning you have seen. The truth hurts.

The number of serious accidents on 20mph roads has increased by 26 per cent last year, according to analysis of government data by road safety charity, Institute of Advanced Motorists.   

Slight accidents on 20mph roads increased by 17 per cent.     

In the same year, there was a decrease in the number of serious and slight accidents on 30mph roads and 40 mph roads.   

Serious accidents went down 9 per cent on 30mph roads and 7 per cent on 40 mph roads.  

There was a five per cent reduction in slight accidents on 30 mph roads and a three per cent decrease on 40 mph roads.    

Even though the decrease in 30 zone accidents is partially because some have been displaced by 20 zones, the imposition of 20 zones has still led to a significant increase in accidents. 

Casualties in 20mph zones also saw a rise. 

Serious casualties increased by 29 per cent while slight casualties went up by 19 per cent.    

IAM chief executive Simon Best said: “The government and councils need to take stock on the effectiveness of 20mph signs. Recent advice, guidance and relaxation of regulations have all been about making it easier for councils to put 20mph limits in place.  “More and more roads are being given a 20mph limit but they do not seem to be delivering fewer casualties. The IAM are concerned that this is because simply putting a sign on a road that still looks like a 30mph zone does not change driver behaviour."   

“More evaluation and research is needed into the real world performance of 20mph limits to ensure limited funds are being well spent. In locations with a proven accident problem, authorities need to spend more on changing the character of our roads so that 20mph is obvious, self-enforcing and above all contributes to fewer injuries. In Europe, it is long term investment in high quality segregated or shared surfaces that have led to a much safer environment for cyclists and pedestrians.”   

Note: an ‘accident’ can cause of several casualties. For example if a bus crashes and kills 30 passengers on board, it is one fatal accident but 30 fatal casualties.         https://www.gov.uk/government/statistical-data-sets/ras30-reported-casualties-in-road-accidents, tables: ras30002, ras30001, ras10002, ras1001

More at IAM


Rod King    on 4 July 2014

This story also came out in 2012 from the Sun. It was investigated by BBC's "More or Less" programme which said that with large increases in 30mph roads being converted to 20mph then the statistics were entirely predictable. It said that any conclusions regarding 20mph limits being more dangerous was "phonus ballonus" because it did not take into account the length of additional new 20mph roads and reduction in 30mph roads. The DfT does not record or issue these lengths.

See the press release from 20's Plenty for Us in response to the IAM at :-


sandford    on 4 July 2014

'Forget all the 20mph campaigning you have seen. The truth hurts'

Ah, headlines worthy of the Daily Express, with the same inattention to facts :) = populist crap from the HJ website editors.
Shows complete and utter lack of understanding of statistical analysis. Poor quality journalism.

JulianTheSceptic    on 4 July 2014

I will come to HJ's defence against the political agitator RK below.

30mph has been the natural speed of urban roads for about 70 years, but anti-car fanatics have been demanding it be reduced in case some inconsiderate pedestrian doesn't pay attention to what they're doing and just dashes out.

20mph zones just give a false sense of security (particularly to those that have been scaremongered). They waste colossal sums of money - £50k for a consultation in Worthing, £350k if implemented, and about £1.2m if 'traffic calming is needed'.

This money could be spent on making road surfaces safer or road safety education. Sometimes it is sneaked from non-council budgets, like the NHS budget in Liverpool.

Elsewhere, these zones are to be imposed although the public was AGAINST them (e.g. Birmingham)

Where authorities have put in speed bumps, this is bad news for ambulance patients who get jarred, and local property owners who suffer from vibrations.

It is about time we saw through the hype.

EndlessWaves    on 4 July 2014

So to refute his point you offer the following claims:

1. One council has at one time been inefficient

2. There was at least two incidences of dodgy dealing (presumably uncovered and those responsible removed from the job and charged, or voted out at the next election).

3. Some but not all types of a different road change cause problems for ambulances

Um, I'm struggling to see how this bears any relation to whether or not the numbers are showing 20mph limits causing more accidents.

The first two are failures with the administrative system and nothing to do with a specific issue. The last one is road-related at least but only touches on the 20mph limit in the sense that it's often used alongside it.

Honestjohn    on 4 July 2014

The point made by RK was already made in the copy above, but not in the IAM release, so RK is obviously responding to the IAM release without reading the HJUK copy.

EndlessWaves    on 4 July 2014

It's still very misleading. Take the line:

"Even though the decrease in 30 zone accidents is partially because some have been displaced by 20 zones, the imposition of 20 zones has still led to a significant increase in accidents. "

To me that sounds like there were more accidents.

Going by RAS3006 we have:
437 serious accidents on 20mph roads increased by 29% since the previous year.
12,158 serious accidents on 30mph roads decreased by 8% since the previous year.

So that means the previous year had 339 serious accidents on 20mph roads and 13,131 serious accidents on 30mph roads.

That's 13470 accidents in the previous year and 12595 accidents in the latest year, a reduction in 875 accidents on 20mph and 30mph roads combined.

I'm failing to see how the imposition of 20mph zones (on 30mph zones) has led to a 'significant increase in accidents'.

Now, if you were comparing an identical set of roads between one year and the next then the 29% increase would be a worrying number but you haven't even reported how the mileage of 20mph zones has changed, let alone discounted any factors that might unduly effect 20mph roads.

A 29% increase in accidents on 20mph roads means there were less accidents if the number of 20mph roads increased by more than 29%

The 'previous year' was 2012 so it could even be that the road closures for the Olympics and Jubilee has a significant effect on the numbers. But I'm sure you can think of much more likely factors that might influence roads that are given a 20mph speed limit more than other roads (road narrowing, speed bumps etc.)

We don't even know how much they vary year by year, perhaps 90 more serious accidents across the entire country from one year to the next is perfectly normal chance variation.

I'm not arguing one way or the other, it may well be that 20mph speed limits are preventing accident numbers from dropping as fast as they would otherwise, or are not changing the numbers significantly and wasting money.

I'm just pointing out that comparing two numbers without accounting for all the other relevant data doesn't tell you anything.

Robwiz    on 4 July 2014

This is spin. It was never claimed that 20 mph speed limits would reduce collisions. The justification for 20 mph zones is that they reduce fatalities, because the probability of a pedestrian surviving if hit at 20 mph is 80%, vs only 20% at 30 mph.

In most urban situations a reduction to 20 mph has no impact on journey times because the average traffic speed remains unchanged. There is, however, a reduction in wasteful acceleration and braking between junctions.

JulianTheSceptic    on 4 July 2014

The experience of localities like Islington and Bath is that drivers tend to ignore the limits.

Police forces like Kent have urged against 20mph zones, and Sussex have suggested that they won't police the zones with any priority. I think that this puts the idea into perspective.

The experience of Portsmouth was that some types of casualties went up, some went down.

20mph zones are still a daft idea because they are a substitute for proper road user education. However if the EU succeeds in getting spy systems built into cars (such as for road pricing), then the authorities will love the prospect at automatic fines every time a speedo drifts above 20, even though there was no danger.

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