Road Safety News
 

RSA sheds more light on streetlights issue

Friday 25th April 2014

Following an article in The Times which suggested that road casualties are rising where streetlights have been turned off, Road Safety Analysis (RSA) has carried out a ‘micro study’ to shed more light on this issue.

The Times' report suggests that there has been a 20% rise in casualties over four years, with 324 more people killed or seriously injured in crashes at night where streetlights were unlit in 2011 and 2012, compared to the previous two-year period.

Using its MAST online analysis tool, RSA found “slightly different numbers when looking at all casualties”, but confirmed that the Times’ statistics were “broadly accurate”. 

However, RSA then went further back to 2005 to see whether this recent increase in casualties was part of a long-term trend (see graph above). This highlighted a big drop in casualties in 2010, probably in part due to the extreme winter weather which occurred that year. RSA’s analysis shows that while there has been an increase in casualties in 2011/12, that increase is only “back to levels similar to those prior to 2010”.

RSA’s micro study concludes: “Of course, The Times’ article was prompted by the decisions made by highway authorities in recent years to turn off or dim street lights and therefore the increase could be seen in this context, rather than the longer period that preceded 2009.

“What we really need to know in order to carry out a robust assessment of this ‘phenomenon’ goes beyond what can be achieved with STATS19 alone.” 

RSA outlines the “data shopping list” it would need to undertake a comprehensive study, and concludes: “Until this is carried out we feel that these results are simply speculation and cannot be regarded as a robust, although The Times should certainly be congratulated for tackling the subject and raising an important issue.”

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We only have 150 words, Hugh, so briefly, collisions are under-reported (except fatal) so your argument seems to be that it's not possible to determine the effect of any intervention. You therefore propose more interventions without evidence and justifying them by opinions. Fine, but whose opinion?

In a scientific trial, otoh, under-reporting is a factor that should occur at both test and control sites and the randomised selection should ensure under-reporting is spread evenly, definitely before the intervention and hopefully after.

Many £millions are spent on road safety so, if the interventions chosen are not the most effective, resources are wasted and lives are lost. Accurate intervention analysis needs to be at the foundation of road safety.
Dave Finney, Slough

Agree (3) | Disagree (1)
+2

I know what is meant by scientific trials Dave, but what I'm asking in the context of road safety is how are you accurately measuring the 'road safety' bit? i.e the resulting accidents or - hopefully - lack of?

We can assess speed, braking distances, braking efficiency, sobriety, visibility, traffic signal phasing etc and lots of other things which are relevant to accidents happening (or not) but we cannot accurately know the actual number of accidents that occurred or didn't occur as a consequence and therefore they won't be 'scientific' results. I know you keep pushing for scientific trials but can't see how the (known) results could be accurate enough to be useful. Sometimes common sense is a good substitute!
Hugh Jones, Cheshire

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-2

What makes it a scientific trial, Hugh, is the randomisation to select test and control. Outside of that, scientific trials are versatile as your metric can be anything you can measure, eg collision rates, burglary rates, cycling/walking rates, local air quality, traffic speed and volume etc.

Scientific trials, Nick, should be used for “site-based interventions that might affect road safety”. In most cases, there are far more sites where RSPs could install their intervention, than they actually do at any one time, eg speed limit changes, visibility barriers at roundabouts, speed cameras, switching off streetlamps etc.

Without scientific trials, RSPs don't have available to them an accurate appraisal method but there is a further big advantage with scientific trials, they can be combined. If councils use them at the local level then, nationally, all the local scientific trials for an intervention can be combined to provide the highest quality of evidence.
Dave Finney, Slough

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+3

Dave:
I think the kind of trials you are talking about would be something to be commissioned at national level, rather than by 'RSPs' (road safety professionals) the vast majority of whom work at a local or regional level.

Road safety officers are primarily involved in road safety education, training and publicity initiatives. They need to be able to identify the need for an intervention, develop the intervention and then evaluate its effectiveness - but that is different (I think) to the kind of scientific trials you are talking about.
Nick Rawlings, editor, Road Safety News

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+2

Dave: In your scenario of the selection of one of two roads, what would actually be measured, or what would you base an appraisal on, that would be a scientific trial?
Hugh Jones, Cheshire

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0

There's a simpler and more accurate method than that, Hugh, which doesn't rely on someone's opinion or best guess. Simply select every site where streetlights could be switched off, select into pairs, and then randomly select one of each pair to be switched off. You now have a “test” group and a “control” group in a scientific trial called a “Randomised Controlled Trial”. It doesn't deal with everything, but it's the best we've got.

If all factors can be measured or eliminated (such as in controlled conditions like test tracks and labs) then scientific trials may not be required but, in the real world, it might be impossible to measure or eliminate a multitude of factors. It's interventions in the real world that scientific trials have been designed for.

Scientific trials are the gold standard for assessing “the effect of an intervention in a complex environment”.
Dave Finney, Slough

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+3

In this context of switching off street lights, the best one could do in terms of a 'trial' is to initially observe whether the driving is more cautious i.e. slower because of the reduced lighting (although complacency and familiarity may cause this to wear off after a short time) and as I said earlier wait twelve months or so(!) and examine accidents that do happen to determine whether they may have happened anyway. As Tim Philpot said elsewhere, driving in the dark on main beam (other traffic permitting) - could actually be better than relying on dim urban street-lighting.
Hugh Jones, Cheshire

Agree (1) | Disagree (3)
-2

Scientific trials are only useful in any context where outcomes can be accurately and unambiguously measured.

Road safety doesn’t lend itself to scientific trials particularly well, especially if evidence is only to be in the form of 'how many accidents?', as there is simply no accurate record of all accidents. If it's resulting casualties we go by, then apart from deaths, we are still apparently not getting the whole picture and resulting casualties can be influenced by many things anyway. Sometimes an intervention such as engineering works can be visually appraised and benefits noticed straight away, but ETP (Education, Training & Publicity) interventions in particular are much harder to assess.

Scientific trials have their place in controlled environments like test tracks and labs when experimenting with new passenger protection devices for instance, but out on the road in real world situations, I think they would be inconclusive.
Hugh Jones, Cheshire

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-2

Good question, Nick. When speaking with RSPs I often mention scientific trials but it's difficult to get a definite answer as to why they won't run them. Difficulties finding matching sites and cost of independent oversight keep coming up but, obviously, those I have spoken with might not want me to name them.

I can understand there are political reasons not to run scientific trials, but I cannot think of any other field of safety engineering where the best quality evidence could be obtained, but the engineers in charge won't run the trials to obtain that evidence.

This seems similar to the development of medicines. Witch doctors found most patients recovered after spells and blood-letting etc but, when scientific trials were used, most patients recovered anyway. That's the point when health care really took off. If we can introduce similarly high quality evidence into road safety, then we might see real improvements.
http://speedcamerareport.co.uk/02_scientific_trials.htm
Dave Finney, Slough

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+5

To address the point Nick poses, given the number of Road Safety Professionals that read this website, perhaps one or more could offer their support (anonymously if necessary) for scientific trials of interventions, or explain why they do not support such trials.
Eric Bridgstock, Independent Road Safety Research, St Albans

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+1

Dave - you say below:

"RSPs seem to be of the opinion that scientific trials are difficult or expensive to run."

Are you able to point to any examples where road safety practitioners have said this?
Nick Rawlings, editor, Road Safety News

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+5

What RSAs analysis, with the list of data still required, and this discussion show is just how difficult it seems to be to determine the effect of interventions when they are not installed within scientific trials. RSPs seem to be of the opinion that scientific trials are difficult or expensive to run. Perhaps this opinion is because no site-based intervention has ever been installed within scientific trials and therefore it is not realised just how easy they are to run? The irony is that it may well be more difficult and expensive to analyse intervention effects when scientific trials are not run!
Dave Finney, Slough

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+1

I thought it would be helpful to respond to Hugh's question about the specific example mentioned by Bob of "a busy roundabout above the M55 and ... also up the slip roads leading to it".

Both the Times' analysis and ours excluded the strategic road network, but defining exactly where this starts and stops is sometimes difficult. Responsibility for slip roads and roundabouts are not always the same - different local agreements may have been reached over the years for different locations, and keeping track nationally of historic changes at all of these in detail for every individual junction is fraught with difficulty.

We use network information supplied to us by the Highways Agency to define the network in England, and also examine the primary road number reported by the Police in order to distinguish crashes actually on strategic roads from those on local roads nearby - on bridges, for example.

It is not for RSA to comment on individual junctions, but whether or not crashes at this sort of location would be counted as 'strategic' and therefore excluded from the analysis depends mainly on whether police crash reports gave 'M55' as the road number.
Bruce Walton, Road Safety Analysis

Agree (2) | Disagree (3)
-1

Interesting point from Tim. If conditions are deliberately made more difficult for drivers by reducing artificial light on urban roads at night, perhaps it does have a beneficial effect by unsettling drivers causing them to think more - not unlike experimental traffic layouts where signing and markings are removed, inducing a state of uncertainty in the driver which should lead to hopefully better concentration and awareness.
Hugh Jones, Cheshire

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+6

Being able to confirm or refute a correlation regarding street lighting and casualties would be a good starting point. However it is perfectly possible to drive safely without street lighting; it is just another circumstantial consideration like wet road surface, and as such can be managed by sensible road user behaviour. The problem, if there is one, may simply be a question of attitude. It is worth contemplating whether drivers, used to a lit road, adjust their speed when it is unlit to allow more time to react to situations developing that are harder to see. Personally I find darkness punctuated by headlights can make some manoeuvres easier rather than harder to judge. By contrast, driving on unlit roads demands more concentration, so there is a greater risk of fatigue. Although ironically, fatigue brought on by a prolonged period of driving on unlit roads might be the cause a collision elsewhere. As usual, no simple answer!
Tim Philpot

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+13

"Further thought - where street lights have been switched off, did any LAs place warning signs for the benefit of motorists? Is there any guidance which says they should?"

I assumed they did - but they were missed in all the darkness.......
Tom - Exeter

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+4

I won't come to Blackpool thanks Bob, nice though I'm sure it is, but I did wonder from your description ('slip-roads') if the roads in question are LA responsibility or Highways Agency? If the latter, perhaps a different criteria was applied. Either way, it would be interesting to know what effect, if any, it has had on the accident record there. As we now have an actual example, perhaps RSA could help?
Hugh Jones, Cheshire

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0

Hugh, come over to Blackpool and I will show you a piece of road that has had its lights switched off at night. It is on a busy roundabout above the M55 and not only around half of that roundabout but also up the slip roads leading to it. It is now in complete darkness and three lanes wide. It's an accident just waiting to happen. I can't even conceive of the notion that staff of the LAs make such safety considerations before deciding which lights to switch off. That would require some forward thinking on someone's part and an understanding of the dangers that it might impose.
bob craven Lancs

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0

Richard Owen is right to point out that the Times data, like his own numbers in his first comment, cannot support the impression given by the report. Apart from ignoring trend and short-term volatility due to weather etc (basic errors which are all too common) they also fail to allow for the increase in roads with lamps switched off.

No one should be congratulated for tackling the issue but getting it so badly wrong. That said I long understood that better lighting does reduce accidents and would be surprised if worse did not increase them.
Idris Francis Fight Back With Facts Petersfield

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-4

Further thought - where street lights have been switched off, did any LAs place warning signs for the benefit of motorists? Is there any guidance which says they should?
Hugh Jones, Cheshire

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0

For any LAs who had decided to switch off steet lighting in some of their roads, the possibilty of an increase in accidents must surely have been uppermost in their minds before doing so, so should they not have been diligently monitoring any subsequent accidents on these roads themselves anyway? They're better placed than a newspaper to identify such roads and decide objectively whether the lack of street lighting actually had a bearing on any accidents that may have happened.
Hugh Jones, Cheshire

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+8