It is a great shame that Paul Pilkington did not reveal his prior
opinions nor declare an apparent commercial interest[1].
Given his prejudice, it is extremely worrying that he could find no
truly substantial evidence of casualty reductions at speed camera sites.
But even if we had excellent evidence of casualty reduction at speed
camera sites that would be insufficient to justify the use of speed
cameras without also considering effects on drivers across the entire road
network.
This is a well known problem. Another paper [2] contains the
following warning: "Consider system effects. Injury prevention measures
may have effects beyond the individual actions they influence directly.
These effects may be harmful or helpful. Always consider potential system
effects."
I am absolutely certain that there are very important and substantial
negative "system effects" relating to speed cameras. I have studied how
drivers routinely avoid road crashes for 20 years and the four critical
factors are undoubtedly: concentration, observation, anticipation and
attitude. Speed in excess of a speed limit is never a critical factor
unless there is also a shortfall in the critical 4. By and large, drivers
make responsible speed choices to the point where causing an injury
collision is a once in 150 year experience for the average licenced
driver.[3]
It is sometimes argued that speed reductions will serve to reduce the
severity of "inevitable" impacts. However, real world average impact
speeds are far lower than the free travelling speeds that might be
effected by speed limits and speed cameras. This is partly because crashes
can only take place where there are road hazards and successful drivers
routinely slow down where hazards are present.
Even after a serious driver error, there is usually time to brake
before impact. The effectiveness of braking before impact is most affected
by the instant of recognition of the problem, and far less affected by a
speed chosen by a responsible driver. In fact speed choice sets the
absolute maximum impact speed, while the moment of recognition often
enables a crash to be avoided completely. The average is between these two
extremes and is far more affected by changes in the moment of recognition
than changes in free travelling speeds.
The bad news for proponents of speed cameras is that, in practice,
they undermine 2 of the 4 critical factors in routine crash avoidance.
Observation is undermined because speed cameras encourage much more
frequent speedo checking (while an experienced driver does not need to
check his speedo at all to drive safely.)
Attitudes are undermined because speed cameras are threatening to
drivers. We can see one example of a serious attitude effect in the under-
researched "race away" crashes described by Chief Constable Richard
Brunstrom in a Times article[4]. He said: "We have a particular problem
with motorcyclists slowing down for the cameras but then speeding up and
dying on the next corner."
Another attitude problem is that many drivers may be deluded into
considering that a speed choice 'must be safe' because it meets legal
requirements. Nothing could be further from the truth - 30mph is
potentially a deadly speed.
If we were eventually successful at reducing speeds generally the
essential process of acquiring driving experience would be adversely
affected. [5] Driving experience is closely related to the key component
anticipation and also affects concentration and observation skills.
The speed camera debate is vast and is far too frequently undermined
by oversimplified thinking. It is only when drivers' thought processes and
routine accident avoidance strategies are carefully considered that the
complete bankruptcy of the technology emerges.
<ends>
[1] http://ip.bmjjournals.com/cgi/content/full/9/4/293
and
http://bmj.bmjjournals.com/cgi/content/full/324/7346/1153/a
and
Rapid Response:
Safe Speed response
It is a great shame that Paul Pilkington did not reveal his prior opinions nor declare an apparent commercial interest[1].
Given his prejudice, it is extremely worrying that he could find no truly substantial evidence of casualty reductions at speed camera sites.
But even if we had excellent evidence of casualty reduction at speed camera sites that would be insufficient to justify the use of speed cameras without also considering effects on drivers across the entire road network.
This is a well known problem. Another paper [2] contains the following warning: "Consider system effects. Injury prevention measures may have effects beyond the individual actions they influence directly. These effects may be harmful or helpful. Always consider potential system effects."
I am absolutely certain that there are very important and substantial negative "system effects" relating to speed cameras. I have studied how drivers routinely avoid road crashes for 20 years and the four critical factors are undoubtedly: concentration, observation, anticipation and attitude. Speed in excess of a speed limit is never a critical factor unless there is also a shortfall in the critical 4. By and large, drivers make responsible speed choices to the point where causing an injury collision is a once in 150 year experience for the average licenced driver.[3]
It is sometimes argued that speed reductions will serve to reduce the severity of "inevitable" impacts. However, real world average impact speeds are far lower than the free travelling speeds that might be effected by speed limits and speed cameras. This is partly because crashes can only take place where there are road hazards and successful drivers routinely slow down where hazards are present.
Even after a serious driver error, there is usually time to brake before impact. The effectiveness of braking before impact is most affected by the instant of recognition of the problem, and far less affected by a speed chosen by a responsible driver. In fact speed choice sets the absolute maximum impact speed, while the moment of recognition often enables a crash to be avoided completely. The average is between these two extremes and is far more affected by changes in the moment of recognition than changes in free travelling speeds.
The bad news for proponents of speed cameras is that, in practice, they undermine 2 of the 4 critical factors in routine crash avoidance.
Observation is undermined because speed cameras encourage much more frequent speedo checking (while an experienced driver does not need to check his speedo at all to drive safely.)
Attitudes are undermined because speed cameras are threatening to drivers. We can see one example of a serious attitude effect in the under- researched "race away" crashes described by Chief Constable Richard Brunstrom in a Times article[4]. He said: "We have a particular problem with motorcyclists slowing down for the cameras but then speeding up and dying on the next corner."
Another attitude problem is that many drivers may be deluded into considering that a speed choice 'must be safe' because it meets legal requirements. Nothing could be further from the truth - 30mph is potentially a deadly speed.
If we were eventually successful at reducing speeds generally the essential process of acquiring driving experience would be adversely affected. [5] Driving experience is closely related to the key component anticipation and also affects concentration and observation skills.
The speed camera debate is vast and is far too frequently undermined by oversimplified thinking. It is only when drivers' thought processes and routine accident avoidance strategies are carefully considered that the complete bankruptcy of the technology emerges.
<ends>
[1] http://ip.bmjjournals.com/cgi/content/full/9/4/293 and
http://bmj.bmjjournals.com/cgi/content/full/324/7346/1153/a and
http://bcc.gn.apc.org/tbc/2002/winter/speedcams.html
[2] http://ip.bmjjournals.com/cgi/content/full/6/2/82
[3] 32million licenced drivers / 214,000 injury crashes in 2003 (source DfT)
[4] http://www.timesonline.co.uk/article/0,,2-1215962,00.html
[5] http://www.safespeed.org.uk/problem2.html
Competing interests: Founder of the Safe Speed road safety campaign.
Competing interests: No competing interests