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Help requested posted on 27th July 2017:

Strobe effect of sunlight through trees causing seizures

I have a road user reporting an infant grandson suffering multiple epileptic seizures due to low sun shining through roadside trees that are set back outside of the clear zone and in neighbouring land parcels. They try to manage it by limiting the light inside the car but this is still not effective. They have requested trees to be set back further but this is very difficult to achieve. Does anybody have any suggestions?

Simon Harrison

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Response posted on 27th July 2017 by:
Saul Jeavons

E: saul.jeavons@transafenetwork.com
T:

Strobe effect of sunlight through trees causing seizures

The issue appears to be one best solved by addressing it with the individual rather than the infrastructure - after all, it would not only be impossible to change all of the infrastructure to remove the cause, but that would still leave it an issue when they went elsewhere.

I'd suggest that the first port of call would be for them to address it with the child's consultant, who as well as medical remedies may know of practical solutions other carers may have found effective.

Next would be for them to identify and avoid the routes in your area which are worst for this problem, and to try to avoid travelling at the times of day when low sun is likely (relatively easy at this time of year, although more problematic as the year draws on). They may find the issue is alleviated significantly by simply avoiding the worst routes at the worst times.

If all else fails then totally blacking out the rear of the car and keeping the child in a rear facing child seat for as long as possible may provide some respite?


Response posted on 27th July 2017 by:
Kate Carpenter

E: kate.carpenter@jacobs.com
T:

Strobe effect of sunlight through trees causing seizures

It sounds as if this is an exceptionally sensitive individual, and the trees are likely to be a small part of their daily visual stimulation. I'd suggest that light-screening within the car (window film/blinds) and/or sunglasses are appropriate, as stimulation could occur in many places. I have extreme light sensitivity with chronic-daily-migraine - which is related to epilepsy in terms of how the visual cortex processes (and is over-stimulated by) incoming light. I'm very sympathetic to the family, but we cannot design or manage road infrastructure to benefit one individual, especially when the in-car environment can be easily managed for children in the back seat. For example if we set trees back and lost the speed-reducing benefit of confined visual corridor we might benefit one person and massively adversely impact many more. Very high-quality polarizing lenses were life-changing for me, wish I'd found them 30 years ago!


Response posted on 27th July 2017 by:
Robert Swears

E: Robert.Swears@opus.co.nz
T:

Strobe effect of sunlight through trees causing seizures

Although my response doesn't directly address the question, the issue identified by Simon also has implications for all road users. Recognising that the seizures are a rare phenomenon created by the strobe effect, the strobe will also be affecting other road users. From a crash investigation perspective, it's important to take into account the conditions at the time the crash occurred; those conditions are not just limited to wet/dry, dark/light, et cetera. We also need to consider temporal effects that occurred at a particular time of day at a particular time of year. While I don't have evidence of a strong correlation, I am aware of high severity crashes that have occurred at sites where there was a strong strobe effect created by sunlight shining through trees. In my opinion, while we shouldn't necessarily be changing roadside features to address the needs of a single individual, we should be considering the wider effects on all road users. I realise that it's not a simple matter of asking an adjacent landowner to cut down trees, however, I consider that environmental effects like the strobe are something we should take into account when we are designing, maintaining, and improving our highway corridors.


Response posted on 28th July 2017 by:
Peter Wilson

E: pwilson@westminster.gov.uk
T:

Strobe effect of sunlight through trees causing seizures

I concur with Saul Jeavons that the best approach would be to address the individual rather than the environment. I have seen a type of blinker as worn by race horses used to overcome stroboscopic images from the peripheral view but have no idea if they work.
That said this phenomenon was identified in France in the 80s with their tree lined straight roads. They added trees into the lines and also removed some to create an irregular pattern which would break up the strobe effect.


Response posted on 28th July 2017 by:
Alex Drysdale

E: alex.drysdale@westberks.gov.uk
T:

Strobe effect of sunlight through trees causing seizures

"They have requested trees to be set back further"... now that has to be one of the daftest and funniest solutions put forward I've ever heard of.

They just need to make a better effort at limiting the amount of light inside the car. I'm sure there's the odd Presidential Limo knocking around with blackout curtains in the back that they could buy...


Response posted on 29th July 2017 by:
Martin

E: martin@userperspective.co.uk
T:

Strobe effect of sunlight through trees causing seizures

Photosensitive epilepsy is typically caused when the flash rate is between 15 and 25 Hz (flashes per second) In some cases it can be between 3 and 60Hz – think of an old CRT type of TV that flickers if you want to get the idea of 60Hz. Different types of seizures exist and there are different occurrence rates between males and females and there is a typical onset age of between 7 and 20 years of age. In road transport its typically only a problem when us science types get people into driving simulators where there are multiple screens that ‘flicker’. So, if its flashes per second that cause the problem then it’s about speed. If you walk along the road then the trees and foliage will cast shadows resulting in a very slow perceived flash rate – if you walk faster than the flash rate will increase. If you drive (increase your speed) then the flash rate is even faster. Simple solution – drive slowly past the trees and the flash rate will reduce. Ideal speed past these trees will depend on the amount of leaves on the trees and the angle of the sun. One other thing to check for is it there is a striped or checked pattern present in the vehicle or the environment. There are some excellent charities that give advice and of course they should chat to their GP. I’m told by some of our military types – exposed to lots of flashing screens – that if you look away – but don’t close your eyes – this can help. I cant comment if this is a good idea.


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