A 55% increase in injury crash risk for Gatso type cameras in motorway road works.


Safe Speed issued a Freedom of Information request to the DfT on July 5th 2005 regarding motorway road works safety. When the results were published on 4th August we were alerted to TRL report 595 "Safety performance of traffic management at major motorway road works".


DfT Freedom of Information response page
TRL595 executive summary
Safe Speed Press Release 228
Safe Speed Press Release 229
Safe Speed Press Release 233 - latest, with full details

And so we purchased the full report. (£40) Upon careful study some 'interesting' data was discovered. It hinges on Table 3.18. We were first alerted to the problem by the footnote, then we looked very closely.

Table 3.18

Some definitions are required to make good sense of this table.

Digital Speed Camera; "Digital cameras described in this study measure the average speed of vehicles over a distance using number plate recognition software." P42 (i.e. SPECS type cameras)

Analogue Speed Camera; "The analogue speed cameras present during this study are those that measure spot speeds of vehicles at a single location." P42 (i.e. Gatso type cameras, and possibly mobile camera vans although these are not mentioned in the report.)

'Other' "... the remaining two sites used patrol cars and speed traps" P42

The figures in the third section 'PIAs' are the personal injury accident rate figures expressed in PIAs per million vehicle kilometres (mvkm). A low figure means lower risk of crashing.
What does it mean?

The 'without speed cameras' figure (the same for road works and open motorway) of 0.089 PIAs per mvkm is a very good general safety performance.

There are six cases where we can see the effects of two sorts of speed cameras and police patrols for both road works and open motorway. As follows:

effect on PIAs Road works open motorway
Analogue speed cameras 55% increase 31% increase
Digital speed cameras 4.5% increase 6.7% increase
Police patrols 27% reduction 10% reduction

These percentages are a simple calculation from the TRL data - for example the Analogue speed cameras at road works is:

0.138 / 0.089 = 1.5506 = 55% increase. 
How might they try to explain it away?

There are limited opportunities to deny the results recorded here, however, we're expecting the camera proponents to try to carry out 'damage limitation' and expect the following claims:

We only placed fixed speed cameras where the danger were greatest, so we should not be surprised that there were high accident rates:

A fairly desperate claim when one considers the three alternatives apparently were better (digital speed cameras, police patrols and no speed cameras!) It's interesting to see them try and use selection bias as an excuse when they have been attempting to benefit from it (via RTTM) for the duration of the speed camera programme.

How has the truth been hidden away?

We have identified no less than 5 different attempts to keep this information under wraps.

1) Report not announced to the public - With the summary report mislinked on TRL web site (here) (at time of writing TRL595 summary link produces TRL594 summary instead!)

2) Report (paid for with public money by the Highways Agency) not available for public download (we had to pay £40 for it).

3) The report's conclusions lump together the benefit of Police patrols (called 'other') with the disbenefit of the cameras to yield a neutral result - as reported in the executive summary.

4) The disbenefit of cameras has not been calculated out, highlighted or made clear  - although the source figures are there.

5) The executive summary comparison groups are not "road works with camera : road works without camera" instead they are "road works with camera : open motorway without camera" this is how they get to claim the 1% and 2% benefits in the executive summary. In fact serious injuries are down in all road works sections irrespective of camera use. 

Casualty severity and speed cameras

The executive summary of TRL595 contains: "...there was a 2% reduction in the proportion of fatal PIAs and a 1% reduction in the proportion of fatal and serious PIAs recorded at sites with speed cameras when compared to the without works period."

Sounds good doesn't it? But they have chosen to compare road works with speed cameras to open motorways. Why didn't they compare road works with speed cameras to road works without speed cameras?

If we examine table 3.10 in the report and calculate the benefits described in the executive summary, we get the table below:

Fatal proportion of PIA Serious Proportion of PIA Serious and fatal proportion of PIA
open motorways 2.7% 14.8% 17.6%
All road works 0.7% 12.1% 13.2%
Road works with speed cameras 2.6% unavailable 17.4%
Apparent change due to speed cameras at road works +271% 1 unavailable  +31.8% 
1 Not a meaningful figure - the number of fatalities in the study was too small.

So speed cameras are also shown to increase the severity of crashes by about 32% 

Summary of TRL595 conclusions

"The study showed that there was no significant difference in the rate of PIAs when road works were present on the motorway."

"The severity and number of casualties were also reduced with the presence of road works."

See the executive summary published by the DfT. (click)

Safe Speed's conclusions

TRL595 is a large scale study - 4 times the size of its recent predecessors. We have absolutely no reason to doubt the honesty of the study because it really does not say what the paymasters would have liked to hear.

Road works are safer than open motorways because although the crash rate is similar, accident severity in road works is reduced.

Speed cameras are very strongly associated with an increase in the number of crashes and an increase in the severity of crashes.

We must remove speed cameras from UK motorways as an urgent matter of public safety.

We must find out who was responsible for keeping this report hidden for 18 months.

We must find out what the Highways Agency have to say for themselves about continuing to use dangerous speed cameras in UK motorway road works.

It is an OUTRAGE that TRL595 didn't fundamentally change the use of speed cameras on UK motorways, and especially at road works sections.

All those drivers convicted in the last 18 months of exceeding the speed limit by speed camera evidence should have their points refunded. Such speed camera operations - known to make the roads more dangerous should NEVER have been allowed.


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Let's make speed cameras as unacceptable as drink driving

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Copyright © SafeSpeed 2005
Created 16/08/2005. Last update 17/08/2005