Cochrane review and meta analysis of studies into speed camera effectiveness

[Hatter The Mad]

A Cochrane review (which goals are to critique papers and research in a particular field as well as provide a meta analysis of them all) was made of 26 studies into the effectiveness (in reducing injuries and deaths) of automatic speed enforcement.

Although individually it found the studies assessed to have weaknesses, the meta analysis shows positive correlation, and recommends deeper studies.

Compared with controls, the relative improvement in pre/post crash numbers resulting in any type of injury ranged from 5% to 36%.

http://www2.cochrane.org/reviews/en/ab004607.html

Twenty-six studies met the inclusion criteria. All but one study reported an absolute reduction in pre/post average speeds. A pre/post reduction in the proportion of speeding vehicles ranged across studies from 5% to 70% depending on the speed threshold set. Pre/post reductions of 50% to 65% were reported in the proportion of speeding vehicles travelling >15 km/h over the speed limit. Compared with controls, the relative improvement was from 1% to 15% for average speed and from 14% to 65% for percent speeding.

All studies reporting crash outcomes reported an absolute pre/post reduction in all crashes and injury related crashes. In the vicinity of camera sites these pre/post reductions ranged from 14% to 72% for all crashes, 8% to 46% for injury crashes, and 40% to 45% for crashes resulting in fatalities or serious injuries. Compared with controls, the relative improvement in pre/post crash numbers resulting in any type of injury ranged from 5% to 36%.

Despite the methodological limitations of the studies reviewed, the consistency of reported positive reductions in speed and crash outcomes across all studies suggest that SEDs are a promising intervention for reducing the number of road traffic injuries and deaths. More studies of a scientifically rigorous nature are necessary to provide a stronger evidence base that these interventions are worthwhile.

 

[End Creditz]

They can be effective when placed, intelligently, around accident black spots rather than in the best revenue generating locations. I suspect with the current cost cutting the latter locations will become more and more heavily favoured

 

[Hatter The Mad]

They can be effective when placed, intelligently, around accident black spots rather than in the best revenue generating locations. I suspect with the current cost cutting the latter locations will become more and more heavily favoured

If the government just put cameras up in accident blackspots, we'd never know if the cameras were actually working because they are there, or whether regression towards the mean was occurring (when something is at its worse, it will naturally regress toward the mean).

http://en.wikipedia.org/wiki/Regression_toward_the_mean

Intuition would say reduced accidents in blackspots that have cameras put up would be because of the cameras, not RTM, though.

 

[Rich_L]

*deafening silence* when it turns out there might be evidence in favour of speed cameras after all

 

[danza]

So, what it's saying is probably what we already knew (although most wouldn't like to admit), that accident black spots can be made safer with the introduction of speed cameras.

If there's a higher frequency of crashes in a particular area, it stands to reason that a form of speed control will at least lessen the severity of crashes, and even reduce the frequency. However, this is obviously dependent on the 'blackspot' on an individual basis, be it a windy piece of road that takes people by surprise, or a busy junction where speed is probably less of a factor in accident frequency.

I think that in some situations they have a valid reason for being instated, but it seems that nearly all of those in my locality are pure cash generators, with not a single camera near to any notorious sections of road. All those I regularly encounter are in 30mph limits in built-up areas (not near schools or suchlike). However, it's nice to be able to potter about without billions of scameras watching your behind, as there simply aren't that many around here.

 

[PMKeates]

I think this tells us that:

• A speed limit does not work unless it is enforced 100% of the time
• The reduction in average speeds when the camera was installed suggests that people were regularly travelling above the posted speed limit before

I suspect people were travelling over the limit through habit. People often assume the limit is below the speed they should be travelling, and travel over it instinctively unless they feel immediately unable to travel at that speed (i.e. a bend looks too sharp, though rarely because of less immediate hazards such as a road crossing or poor visibility at a junction). Having limits sets a target for people and makes them assume they do not need to make their own judgement on speed or really pay much attention to what is going on.

 

[Dolph]

If the government just put cameras up in accident blackspots, we'd never know if the cameras were actually working because they are there, or whether regression towards the mean was occurring (when something is at its worse, it will naturally regress toward the mean).

http://en.wikipedia.org/wiki/Regression_toward_the_mean

Intuition would say reduced accidents in blackspots that have cameras put up would be because of the cameras, not RTM, though.

But that is exactly what happens already camera sites have to have a recent history of accidents/deaths (although as the M4 camera showed, they don't have to have anything to do with speeding).

Failure to account for regression to the mean is a consistent failing of most speed camera research in the UK, and as soon as the government actually started taking it into account, the effectiveness dropped dramatically from the previous claims.

The other question not addressed by the report is how speed cameras compare to other methods of awareness control (which is what speed cameras are ultimately supposed to be).

I've never been entirely opposed to speed cameras when used correctly, the problem is that cameras haven't been used correctly, and the road safety message being embraced from the government down is fundamentally flawed if you want to reduce accidents, because exceeding the speed limit has a very small (circa 5%) contribution to accidents. If you want to reduce accidents, you tackle the causes of those accidents, not a minor sideline that just happens to raise money.

 

[Lowe]

If you want to reduce accidents, you tackle the causes of those accidents, not a minor sideline that just happens to raise money.

That's exactly what's annoyed me so much over the years. If an area has a black spot for accidents, do something about the black spot itself! Change the junction for something else, introduce some kind of traffic management at that point, etc.