Thursday, 17 November 2016

Misleading Odds of Dying

There have been various claims in the media and research about the efficacy of cycle helmets lately.

One such article of note, was from 2012, Nonuse of bicycle helmets and risk of fatal head injury: a proportional mortality, case–control study, by Navindra Persaud et al., which claims that you're 2.5 times more likely to have a fatal head injury as a result of not wearing a helmet, with an odds-ratio increasing to 3.1 when "adjusted for age and sex".
Results: Not wearing a helmet while cycling was associated with an increased risk of dying as a result of sustaining a head injury (adjusted odds ratio [OR] 3.1, 95% confidence interval [CI] 1.3–7.3). We saw the same relationship when we excluded people younger than 18 years from the analysis (adjusted OR 3.5, 95% CI 1.4–8.5) and when we used a more stringent case definition (i.e., only a head injury with no other substantial injuries; adjusted OR 3.6, 95% CI 1.2–10.2).  
This study was note worthy as it was the first research into fatal head injuries that had any significant numbers and possibly proved the efficacy of helmets. And as always, when ever an article like this is published, within microseconds of the abstract being made public, the media were quick to promote it. So how was this reported by the papers?

Cyclists without helmets TRIPLE their chance of death by head injury ...

The suggestion by the abstract and the media is you're three times more likely to die without a helmet....

This Is Possibly Misleading...

But to be fair to the Star, the abstract is not easy to interpret, and most people would possibly come to (incorrect) conclusion that if you dont wear a helmet you'd be three times more likely to die, than if you did, when in fact the result pertains to fatality by head injury, not overall fatality,  i.e. where someone would have died regardless of whether they did or didnt suffer a head injury.

Is it possible to use their result to obtain the actual odds ratio for dying with and without a helmet? Yes.

There was 129 cycling deaths studied by coroners in Ontario from 2006-2010. Out of these deaths, 34 cyclists wear wearing helmets, and the rest, 95 cyclists were not wearing a helmet.

In studies like this, in order to estimate an odds ratio, a control group is required. Some of the fatalities need to be placed into a 'cases' group, and some need to be placed into a 'control' group. The control group effectively gives you the odds that someone was wearing a helmet. Autopsies were conducted to determine the cause of death, and as I understand it, the pertinent groups were
  • death due entirely to other injuries, regardless of head injury
  • death entirely and solely due to a fatal head injury, without other fatal injuries
  • a fatal head injury with other injuries
The first of the above list comprised the control group for the first row of their results table (shown below). Helmet wearing for the controls was around 36%, which they claim to be consistent with a 2009 survey. In their second row, pertaining to pure head injury (no other injuries) they also claimed to have measured the same helmet wearing ratio of around 36%.

Their results are in table 3, and are thus:

Odds of death from a head injury when not wearing a helmet while cycling, with and without other substantial injuries
Case definitionFraction not wearing a helmetOR (95% CI)Adjusted*
OR (95% CI)
Head injury as cause of death with other injuries58/7137/582.5 (1.2–5.7)3.1 (1.3–7.3)
Head injury as cause of death with no other injuries38/4357/863.9 (1.4–10.9)3.6 (1.2–10.2)
Note: CI = confidence interval, OR = odds ratio.
*Adjusted for age and sex.
As explained above these results are NOT THE odds ration for dying with and without a helmet, they pertain to fatal head injury.

Take row 2 for example, it means out of the group that died solely as a result of a fatal head injury, the odds-ratio was 3.6. But note the controls! 86 people out of the 129 died as a result of other injuries. They would have died anyway, helmet or no helmet.

How do calculate the actual odds of dying in without a helmet from the above data for the cyclists in this study group?

Simply as:

(95/34) x (0.36/ (1 - 0.36)) = 1.57

Where 0.36 was their measured helmet wearing rate in the controls, and as above, a total of 95 cyclists were not wearing a helmet, but 34 were.

Caveats, this odds ratio is pertinent to crashes of this severity, and is subject to the controls being correctly identified. A small bias in mis-classifying the controls, has a drastic effect on the supposed odds-ratio. This ratio also pertains to riding conditions in Ontario, where 78% of the victims were involved in a collision with a motorised vehicle.

Are Persaud's Results valid?

Many studies and researchers have found that drunk cyclists are very unlikely to be wearing a helmet. Out the 129 victim's in Persaud's study, 30 were drunk.
Just let that sink in....

Others have rightly criticised the study for not accounting for intoxicated cyclists.

If those drunk cyclists were removed, the confidence intervals for the study would no longer be significant! Equally, if all those drunk cyclists were in the 'cases' group and not distributed appropriately to the control group, then the reported odds ratio would decrease significantly.

Tuesday, 26 January 2016

The Richard Wellings' Dodgy Calculator

A 2 minute delay equals a £16 billion loss per year. This sounds like bullshit....

Well, if there's 33 million vehicles in circulation that's 66p per minute of delay.

16000000000/365/33000000/2 = 0.66

66p is the equivalent of an £84k annual salary (0.66 x 60 x 40 x 52)

However, not all 33 million vehicles are on the road at the same time, even in rush hour. So the £84k rate has to be a bare min.

So Wellings believes that your time in a car is worth much more than £84k per anum.

To further demonstrate what garbage this is, if you drive an hour to work an hour back each day that's approximately equal to £20K per anum (60x0.66x52x2x5).

Anyone out there being paid £20k a year for just driving to work? Or "losing" £20k a year because they drive?

What about professional drivers such as hauliers? They're paid for driving, obviously, but unless I greatly mistaken do you know any hauliers that are paid greatly in excess of £84k a year?

Of course Wellings doesnt publish his "scientifically peer reviewed" calculation - it's only available by private communication with him....

So may it's just bullshit...

Friday, 12 December 2014

The cyclist should have been paying more attention

My commute takes me over a short hill, as I approach the crest of the hill my speed drops to around 14 mph. A second later though as I emerge over the other side I very quickly reach around 25-30 mph but am routinely held up by parked cars or vehicles that I catch up. For this reason and the fact the hill crest is on a blind corner, there is very little point in cars trying to overtake me on this section, and frankly it's dangerous. In fact the ones that do either put my life at risk because they have to cut in at high speed and slam their brakes on, or more usually they chicken out because they find themselves on the wrong side of the road doing around 35 mph into on coming traffic.

Today I was commuting as normal, and as is typical people in cars were being slightly bullish, one was trying to overtake me at this very point I've described. I hold out my hand to point out that there is on coming traffic. They slow down and thankfully dont overtake, I briefly look over my shoulder to double check. I now have a tailgating motorist closely following, and is preoccupying my mind.

Around a second later as I am gaining speed down the hill I see a car is trying to reverse out of the junction. That's concerning! I have a tailgater which I'm trying to mitigate against by keeping my speed reasonably high, but I also might need to slow in case this the reversing driver hasnt seen me. There really isnt much time to think about these things, but I cover my brakes and slow a fraction doing my best to juggle in my head whether it's better to slow or maintain speed because of the tailgater.

Whilst this is happening I can also see that there are parked cars ahead, and traffic is slowing for them. I'll be at that queue in a few seconds. My mind goes to the tailgater. Is he going to overtake and slam his brakes on. Is he a Must Get In Front driver? But crucially I also havent taken my eye or mind off the reversing driver. They have stopped reversing.

Thank fuck for that.

I look over my shoulder to check the tailgater, I then look forwards again to check the queue of traffic...

then I realise - my heart sinks - ARGGHHHHH

I've missed a massive hazard. There is an oncoming car that has it's indicators on, and wants to turn right and park on my side of the road. It's twitching to move. So is my arse. I have only just seen this car. It might be moving.

All of this has happens within a 7-10 second window.

Whilst I was concerned with the brow of the hill, the tailgating car that was trying to overtake, the car beginning to reverse out of a junction, the queuing traffic behind a parked car, and the usual task of picking a line though a pothole ridden UK street - I had not been paying enough attention to a car that looked like it might be turning across my path.

How many fucking things have I got to watch out for - I cant watch everything on the road. I cant mitigate and counteract every single possible hazard. There are only so many things one can juggle in their head within such a time frame. It was also an impossible balancing act of choosing what speed would keep me safest.

Nothing happened.

The car stopped rolling.

It was just another commute.

But what if this driver hadnt have stopped? What if he turned across me?

I probably would have slammed my brakes on, and about 1-2 seconds later likely collided.

What if I had recorded the incident on youtube? What would uninformed viewers think? Viewers that had no idea what hazards were already preoccupying and burdening me.

They would say, the cyclist should have seen it and predicted it all. He should have slowed. It's obvious. Sitting there with the benefit of hindsight, but uniformed of the actual situation......
I fear some might have unwittingly victim blamed me.

I am a defensive cyclist. I routinely look over my shoulder, look for cars pulling out of junctions, fear left-hooks, and try to mitigate against must-get-in-front overtakes that end with drivers slamming their brakes. But there is only so much that one can consider and at any given time and if there are too many dangers in one situation it's impossible to counteract or see them all.

Whilst the severity of some situations could be lessened by being a more defensive cyclist, there's only so much that a one can do to defend against bad driving....

Sunday, 10 August 2014

The cost of the Sheffield Tram

The question is: Why is spending money on the tram deemed a success, yet spending equal amounts of money on cyclists is unaffordable?

Concerning the Sheffield Tram system, how much has each two-way journey cost the tax-payer, and why are similar investments not being made for cycling?

The South Yorkshire Passenger Transport Executive (SYPTE) paid £240 million for the tram system in 1994. In the first couple of years it was a deemed a failure, and was sold to Stagecoach in 1997, for the pittance of £1.15 millionHowever, more and more people now use the tram, with 15 million journeys per year, and it is now considered by some councillors an environmental, and transport success.

In the years 1994 - 2014, the total number of hop-on journeys was 230.5 million. So when adjusted for inflation (£240m -> £426m), each two-way journey has been subsidised by


This assumes that Stagecoach dont pay anything for the tram other than the initial leasing cost £1.15m, and as far as I'm aware, they dont. In fact the SYPTE are currently funding a £32 million improvement.

This seems like quite a lot of money to be paying for each two-way journey, but I have no problem with that as it's a sustainable mode that gets some people out of cars. However, I'd like to know why, at this cost, the tram is deemed a roaring success yet our councillors and government will not fund decent quality cycle infrastructure with the same financial parity.

In fact, in a recent discussion a councillor, Jack Scott, said it was right to remove a key cycle-way which circumnavigated the dangerous Brookhill roundabout, to make way for the tram. This infamous featured as a prominent #cyclesafe cycling horror story in The Times.

Tweet, arguing that he tram has been a success, "envied by many":

In Sheffield there are around 4500 routine cyclists, and this number is growing. If, like the tram, we spent £3.70 per two-way journey per cyclist over 20 years, we could build a staggeringly good cycle-network that would attract many more cyclists and would indeed be truly sustainable transport.

4500 x 365 x 20 x 3.70 =
 £121 million

So the question is again: Why is spending money on the tram deemed a success, yet spending equal amounts of money on cyclists is unaffordable?

Saturday, 9 August 2014

Balancing Segregation against Vehicular Cycling

Why segregate? There is really only one answer to that question - motorised vehicles. Cycling is safer and far more enjoyable the further away you are from motorised vehicles. This is true even for roadies, like me, who seek out quiet lanes and roads that have very little traffic. However, there are many advantages to using the road system over the current mess of cycle-paths we have in the UK, because the way segregated paths are implemented in the UK is exceptionally poor.

The reason for writing this post, is a new cycle-path has just been constructed in the Peak District between Bamford and Hathersage. In theory it should be a welcomed addition because it is very well surfaced and reasonably wide, yet not all cyclists are using it, and the vast majority continue to the use the road. So why are the cyclists, including myself continuing to use the road?

Aside: Before continuing, take note, this is not a post that is pro Vehicular Cycling over segregation! It's about why UK segregation fails, and what's needed to fix it, and the massive trade off that is made when using the path over the road.

The answer to the above question, is quite simple, this particular road, despite being 50 mph, is perfectly fine cycle on. It already has a wide cycle-lane, and it is therefore less convenient to use the new shared-path. The shared path is only on one side, so cyclists on the opposite side have to cross the road - twice! They have to give way at junctions, and the path ends before Hathersage, where cyclists are forced to give way to cars, whereas if they have stayed on the road they could have continued uninterrupted!

Despite the above problems I sometimes use the new path, and when on it, it's actually quite nice to be segregated from the cars. However, that one, single, plus point is heavily traded against many other problems. If we list the good and bad points of using the road verses the cycle path, the two list are significantly skewed.

Riding on the Road

Good points:
  • Cars have to give way to cyclists. You are a vehicle that has the same "rights".
  • No loss of priority at junctions and roundabouts.
  • No pedestrians on the road (at least rarely).
  • Convenient and continuous.
  • Extensive network.
  • Usually a smooth tarmac surface, swept free from debris. Gritted and cleared in the winter
  • Roads are very well signed and mapped.
Bad points:
  • You are a vulnerable user

Good points:
  • Cycling in a space away from motorised vehicles
Bad points [regressive UK implementation]:
  • Loss of rights at junctions - you now have to give way at junctions
  • If you make a mistake giving way and get hit by a car - it's your fault!!! UK laws do very little, if anything, to protect you in this scenario.
  • These junctions have been built with cars in mind, not bikes. That means fast, rounded corners, and wide junctions, that can be difficult and sometimes dangerous to cross.
  • Shared with pedestrians, and dog walkers, who are usually oblivious to cyclists. Risk of collision, and you have to greatly reduce your speed.
  • Surfaces are usually worse than the road, debris, and rarely gritted in winter.
  • Massively disjoint network. One minute you are on a wide reasonable path, next it's narrow pavement and a dismount sign, thrusting you off the path at a dangerous junction.
  • These paths rarely transition from the road nicely.
  • Continuation and mapping of cycle-paths is awful. You have to have local knowledge to know where the paths are and where they go, and crucially where they cease or become unsuitable for say a road-bike.
It seems the only bad aspect of using the road is your vulnerability as a cyclist. Segregation is meant to fix that vulnerability, however, it is quite clear that in doing so it completely erodes all of the positives from using the road, and replaces them with many negatives and a whole set of new vulnerabilities - like being forced to cross the road at terrible places where you have lost the right of way and any protection in law.

Without question the way in which many UK cycle-paths are implemented is all wrong. All the above negatives does not mean I'm against infrastructure and segregation, because quite clearly many roads in the UK are not fit or pleasant to cycle on. I'm against the current regressive and awful implementations we have in the UK.

If we were to look at the infrastructure in the Netherlands the above negative points would be completely different! All the bad points would be flipped into good points
  • In the Netherlands there is no loss of rights, at many junctions cars give way to cyclists.
  • The law and design of the junctions protects the cyclists: They have presumed liability.
  • Junctions have been built and designed with bikes in mind, not just cars.
  • They are not usually shared with pedestrians. Cyclists have their own roads.
  • They are gritted in winter and high quality surfaces.
  • I dont think there's any such thing as a dismount sign in NL.
  • These paths are always linked up and transition nicely - they dont just spit you out at a horrific junction with only the road as an option.
  • Mapping is supposedly not a problem, they are well signed, and dont run out or turn to gravel or a muddy field.
So why are many cyclists continuing to use the road instead of this new path? Simple, the trade off is not worth it. Why leave a perfectly reasonable road for a path that is less convenient and actually places you in more danger when trying to cross two lanes at the end of the path.

In the Netherlands, by all accounts, they dont have these problems because they did things correctly. The trade off isnt compromised, they have segregation from cars, but crucially they dont have all the negatives that the UK paths have.

If this path had been built in the Netherlands, there would be no give way and dismount for the gates into the farmer's fields. The path would be continuous through the major junctions, with traffic lights for the cyclists. The path would also be continuous into and through Hathersage, with traffic calming for cars.

Instead, the path starts abruptly and ends abruptly making the transition onto and off the path more arduous and frankly dangerous than just staying on the road. There is nothing whatsoever to traffic calm cars at the start and end of the path.

I'm not against segregation, because I strongly believe some of the busier A-roads into the Peaks should have wide segregated cycle-paths, but the current UK implementation continues to be shoddy and panders to cars. Until that culture is changed it will be difficult to achieve the infrastructure they have in the Netherlands.


Thursday, 26 June 2014

Helmets are a Distraction

In my opinion the discussion surrounding helmets and the obsession by some calling for them to be mandatory is a massive distraction from the real issues concerning cycle safety. In countries like the Netherlands virtually no one uses helmets and yet the rate of deaths and injuries compared to the UK is practically an order of magnitude lower.

It is blindingly obvious that real safety will come from providing proper dedicated Dutch style  #space4cycling and improving the behaviour of motorists around cyclists. Risk of injury imo is due to frequency of errant interactions between motorists and cyclists, and cyclists being forced to use inappropriate roads. i.e the more close passes you experience the more likely you are to get injured, and similarly cycling on busy/fast roads is riskier than using a good quality well designed cycle-way.

If we can improve the above situations then safety will increase considerably, and that imo would dwarf the small numbers that might be saved be by forcing everyone to use a helmet. No country has yet demonstrated a plausible or significant increase in safety with mandatory helmets*.

Below is an ad-hoc calculator to estimate how many would be "saved" by forcing people to wear helmets if helmets really did protect against serious injuries, and how many would be "saved" by improving overall safety through #space4cycling and/or driver behaviour.

Current situation:
Percentage of journeys by bike
Percentage of people using helmets
Current deaths
Current serious injuries

Magic plastic hats:
Percentage that would be "saved" by using a helmet

#Space4cycling and improved road conditions
Safety Multiplier, how much safer it could be

What if more people cycled (like in Holland):
Percentage of journeys by bike

Injury rate vs cycling rate:

"Safety in numbers" fudge factor

Tuesday, 17 June 2014

Cyclist Driving Sight Distance Calculator

If you are driving and have to slow down behind a cyclist because it is not safe to overtake, how much sight-distance is required?

Braking fraction 0.7
1.0 is hard braking, less 0.5 soft braking
Thinking Time 0.5
in seconds

Visibility distance (metres) needed for Bike Speeds (mph) vs Car Speeds (mph)

Braking fraction, 1.0 is emergency stop braking based on approx rates from Highway Code. Friction=0.7
Car speed is from left to right, bike speeds increasing downwards:
Thinking times: competent reaction times are usually mush less than 1.0s