An interesting essay on crashes with good visibility

[PhilO]

I've just been reading this on STW, and thought it would be of interest here.

http://singletrackworld.com/2018/01/collision-course-why-this-type-of-road-junction-will-keep-killing-cyclists/

There's a thread here concerning one of the accidents mentioned in Bez's article, but I thought it better to start a new thread.

[mustgettaller]

Very interesting.

As a sailor and former pilot, I'm very aware of the constant bearing trap. The Air Force had (and probably still have) posters saying "The one you can't see will kill you" - i.e. the plane on a constant bearing is almost invisible.

Thinking about how I ride, the article has made me realise that when I'm out cycling I am often thinking of whether I am crossing a driver's field of vision at similar junctions, or whether I'm hiding in a potential pillar blind spot.

I also know this junction well. The solution seems elegant - and not dissimilar (I think) to quite a lot of junctions one sees where a curve has been put on the approach, except I think in most cases to force traffic to slow down.

The article also underlines the point that quite often accidents are a confluence of several factors - not just "a car driver driving badly". Not to say that there are too many where the cause is just that.

[Kim]

As a cyclist I'm distinctly aware of A-pillars of vehicles approaching junctions.  There's a roundabout I cross regularly where the wrong combination of speeds keeps the pillar of an approaching vehicle between the driver's eyeline and mine for several seconds as they approach the entrance to the roundabout - exacerbated by it being a large roundabout with fastish traffic, where your normal cyclist's self-preservation instinct is to go as fast as possible.

When driving, I move my head to see around the pillar in those sort of situations.  I can't honestly say I'd be as prudent if it was as open and boring as the junction described in the article, though I'd still slow down for the give way line.

Discussion of the article on twitter also raised the issue of Polder Blindness^[1] - a psychological phenomenon rather than a physical one, but relevant to the same sort of situations.


_{[1] The English-language version of the page points to Highway Hypnosis, which suggests the effect is safety-neutral.}

[Cudzoziemiec]

That's an interesting and clear explanation of the problem (as Bez tends to do). It occurs to me there might be a third solution to the problem; it's not always (in fact it's usually not) going to be possible to remodel junctions as suggested, and however well we train drivers we tend to lapse into less demanding ways, but if we replaced all Give Ways at similar junctions with Stops, that would force a change of relative bearing – and give drivers an instant to look around. ISTR that in Denmark(?) all "give way" lines are actually Stops.

[hellymedic]

Bez has written an excellent piece.

Many disasters result from the confluence of multiple 'minor' factors making a 'perfect storm'. The 'Give Way' at Ipley Cross has been replaced by 'STOP' but compliance is variable (and enforcement non-existent) so lives will be lost here again until the junction is remodelled.

[Kim]

The 'Give Way' at Ipley Cross has been replaced by 'STOP' but compliance is variable (and enforcement non-existent) so lives will be lost here again until the junction is remodelled.

It needs Silly Sustrans Gates™, obviously.  Won't be any crashes due to failure to give way if drivers have to get out and carry their cars through an awkward gap on both sides of the junction.

[mrcharly-YHT]

Severe speed bumps at every junction

Might not make people stop, but at least it will make them slow down, rather than flying across

(I like the silly sustrans gate option tho')

[Si S]

Severe speed bumps at every junction

Might not make people stop, but at least it will make them slow down, rather than flying across

(I like the silly sustrans gate option tho')

Traffic calming measures are only allowed in street lit areas because motorists have no means of making things like warning signs or road markings visible in the dark

[mrcharly-YHT]

Severe speed bumps at every junction

Might not make people stop, but at least it will make them slow down, rather than flying across

(I like the silly sustrans gate option tho')

Traffic calming measures are only allowed in street lit areas because motorists have no means of making things like warning signs or road markings visible in the dark

Laws can be changed you know

[mattc]

Severe speed bumps at every junction

Might not make people stop, but at least it will make them slow down, rather than flying across

(I like the silly sustrans gate option tho')

Traffic calming measures are only allowed in street lit areas because motorists have no means of making things like warning signs or road markings visible in the dark

'm going to assume that Si is aware of car headlights, and thus his comment was probably in jest.

[Si S]

Severe speed bumps at every junction

Might not make people stop, but at least it will make them slow down, rather than flying across

(I like the silly sustrans gate option tho')

Traffic calming measures are only allowed in street lit areas because motorists have no means of making things like warning signs or road markings visible in the dark

'm going to assume that Si is aware of car headlights, and thus his comment was probably in jest.

Apologies, insert smiley of choice

[JennyB]

The dangers of crossroads (if not for these reasons)  have been known and quantified for at least* 50 years:

Lay out the road system so that any two roads which meet at grade, meet in three-way T junctions as near 90 degrees as possible. Avoid four-way intersections and crossing movements.

This follows from the geometry. Where two two-way roads cross, there are 16 major collision points, compared with three for a T junction (John Callendar, Time Saver Standards, Fourth Edition, New York, 1966, p. 1230).

Referenced in Pattern 50 of Alexander's A Pattern Language

That's why offset crossroads have been standard in the Republic of Ireland for as long as I can remember.

* In folktales you often meet the Devil at a crossroads.

[DuncanM]

While changing the road layout would definitely work, surely the simplest cheapest solution is to plant some trees or put some other sort of barrier up so that the sightlines are bad? That forces anyone approaching the Stop sign to slow right down, because they can't possibly see if there is something coming.

[Cudzoziemiec]

* In folktales you often meet the Devil at a crossroads.

They seem to have been a common site for gallows too.

[hellymedic]

While changing the road layout would definitely work, surely the simplest cheapest solution is to plant some trees or put some other sort of barrier up so that the sightlines are bad? That forces anyone approaching the Stop sign to slow right down, because they can't possibly see if there is something coming.

This may, or may not work.

There are many crashes in which the driver 'didn't see' the victim. Assuming a clear path is not the same as seeing a path to be clear and this has had lethal consequences in fog, dark and with 'hidden dips'.

[DuncanM]

While changing the road layout would definitely work, surely the simplest cheapest solution is to plant some trees or put some other sort of barrier up so that the sightlines are bad? That forces anyone approaching the Stop sign to slow right down, because they can't possibly see if there is something coming.

This may, or may not work.

There are many crashes in which the driver 'didn't see' the victim. Assuming a clear path is not the same as seeing a path to be clear and this has had lethal consequences in fog, dark and with 'hidden dips'.

True, though the problem with "hidden dips" at least is that those give the appearance of being clear.
I have noticed that a number of roundabouts near Northampton have had extra fences erected to ensure that you can't see onto the roundabout until you are very close to it. That means you have to slow down more on the approach. I found them annoying at first, but then I understood how removing sightlines can increase safety.

[Cudzoziemiec]

What these crashes have in common with hidden dips, fog, etc, is that there is a difference between "not seeing anything there" and "seeing that there is nothing there", and sometimes that difference is fatal.

[hellymedic]

What these crashes have in common with hidden dips, fog, etc, is that there is a difference between "not seeing anything there" and "seeing that there is nothing there", and sometimes that difference is fatal.

Too true!
 

[fruitcake]

Bez has a blog entry dealing with alternative solutions, including a roundabout, speed bumps and fencing. He claims the most cost effective solution is breaking this crossroad into two T junctions as illustrated in his original essay.

[Asterix, the former Gaul.]

The dangers of crossroads (if not for these reasons)  have been known and quantified for at least* 50 years:

Lay out the road system so that any two roads which meet at grade, meet in three-way T junctions as near 90 degrees as possible. Avoid four-way intersections and crossing movements.

This follows from the geometry. Where two two-way roads cross, there are 16 major collision points, compared with three for a T junction (John Callendar, Time Saver Standards, Fourth Edition, New York, 1966, p. 1230).

Referenced in Pattern 50 of Alexander's A Pattern Language

That's why offset crossroads have been standard in the Republic of Ireland for as long as I can remember.

* In folktales you often meet the Devil at a crossroads.

The French are much more likely to give cross roads STOP signs.  They are also likely to monitor them and prosecute drivers who they see fail to stop for the prescribed 3 seconds.

Drivers do tend to stop at them, possibly to see if a gendarme is watching.

[dim]

speed bumps and 4 way stop signs .... that's what works in South Africa

[benborp]

The French are much more likely to give cross roads STOP signs.  They are also likely to monitor them and prosecute drivers who they see fail to stop for the prescribed 3 seconds.

Drivers do tend to stop at them, possibly to see if a gendarme is watching.

A time isn't specified in 'le code de la route' nor the legislation. It is the same as the UK in that the vehicle must come to a complete stop but for an unspecified time. Good luck putting that to a gendarme though.

[Asterix, the former Gaul.]

When I say 'prescribed', it was an in-law who told me.  He is a highly experienced motorised traveller having, among other things, toured the Middle East on a motor bike (for which at one point he was offered many camels).  He also smuggled currency from Greece into Albania on it for entirely altruistic reasons.  I have never read the French highway code but many ex-pats have confirmed that it is wise to stop at STOP signs.

When i took my motorbike test in the UK, the advice was to put a foot to ground as proof of stopping.  I'd guess that'd have taken me at least three seconds.

[mustgettaller]

All going a bit off topic here but...

WRT stop signs. A fee years ago I hired a bike in Austin Texas. As a visiting Brit I asked if there was anything I needed to know about local cycling culture and laws. I was told that at stop signs one must put a foot down (even just a dab) to show you  have 'stopped' - otherwise expect an on the spot fine from the zealous local law enforcers.

I then set off on a 50 mile ride which became an audacious 115 miles in 30 degree heat. But that's another story. 

[MikeFromLFE]

All going a bit off topic here but...

<snip> I was told that at stop signs one must put a foot down (even just a dab) to show you  have 'stopped' - otherwise expect an on the spot fine from the zealous local law enforcers.

My recollection is that what the UK rules* require - this memory (possibly false) goes back to when I used to ride with a CTC section in the 70s (and when we had road rules in the UK that were enforced).
*It may not be a law, but how the law is interpreted.