BMW: please don't drive like utter wankers

As the arrogant self entitled owners of an Important Car for Important People, we recently received a communication from the manufacturer. Here it is, unabridged

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Dear BMW Owner

Due to the large number of people who have been killed recently by drivers —especially pedestrians and cyclists in hit-and-run incidents— the transport minister Jesse Norman has been in touch with us. He would like to pass on a message

"It’s great that driving has become so popular in recent years but we need to make sure that our road safety rules keep pace with this change.

"We have some laws that ensure that drivers who kill others are rarely punished, but, given recent cases, it is only right for us to look at whether dangerous drivers should face the consequences."

We at BMW would like to remind our drivers that all of us are representatives of the BMW family; whenever one of us drives like an utter wanker, we are all tarred in the brush of shame. We must strive to ensure that the badge of utter-wanker-driver continues to be held by Audi drivers alone.

Please, study the highway code, and remember that you should be prepared to stop at "Give Way" signs rather than slow down slightly. In particular, when joining a roundabout you are expected to yield to all users, including cyclists. The Highway code also covers other signs worth learning, what the orange light in traffic lightss, and the rules of zebra crossings.

The next time your BMW is due in for a scheduled service, please get in touch to attend one of our free "safe BMW driving" seminars, whose topics include:

1. Speed limits: what, why and how.
2. Indicators: the politer way to communicate.
3. Overtaking: when you shouldn't.

We also offer to recalibrate the speed warning to 90 mph —just ask the service team to lower it.


Finally, when on a motorway, please leave at least two metres difference between you and vehicle in front —even when an owner of Ford Fiesta has mistakenly pulled into the fast lane while only doing 75 mph. It's safer for everyone.

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There you have it. We'll try and drive better than others, and even explore the do-not-disturb option or our phones. We should be able to keep it up for a few weeks to see whether you can get used to it. Motorway speeds are probably going to be the tough one, given that even Corsa drivers will end up passing us —that's not what we paid for.

PS: Why are we getting email from Jaguar Land Rover Australia saying "Congratulations on the recent purchase of your Evoque, and welcome to Land Rover."? Some mistake surely.

Stopping distances experiment #2: The real world

Last week we discussed a (flawed) stopping distance experiment, where we argued that you cannot stop from 18 mph to 0 in 6.5 metres, no matter what the police claim. That's when you are prepared to halt and planning the exact moment to pull on the levers.

What does it a real emergency halt look like? It looks like this video. Taken about half an hour before the one of a BMW driving down a pavement to get past a traffic queue, for reference.

Here is what it looks like when someone runs out in front of you while you are freewheeling down a hill (Hampton Road, BS6). Speed? Let's assume 18-20 mph. You can hear from the noise of the (hope) hubs that there's no pedalling, so this is just a gentle 5-10 mph curve round the mini-roundabout-of-death, a few spins of a drivetrain in precisely the low gear you are always in when you come up the hill from the Arches, and then coasting, relying on gravity to do the work.

• 0:26 small kid runs out from some cars, looks like 3 parked car spaces away. Assume: 12-16 metres.
• No previous visibility, on account of the cars being bigger than him.
• 0:27 cyclist sees this and shouts "wooah!"
• 0:28 bike catches up with where kid was: he's run on to be with his friends. (Assuming 16 metres, that puts velocity at 29 km/h)
• 0:29 cyclist has now slowed down to the kids running-along-the road pace. Asks child to look. Child doesn't appear to hear them.

The entire incident is over within five seconds. There wasn't enough time to slow down before any collison would have occurred. Shouting and swerving while you slow down is all you have.

The gradient of the hill will have made stopping hard, and this wasn't the "prepared for emergency brake" setup of our previous experiment. This is real world going round the town with your hands on the tops of the levers, with gravity fighting the decelleration. The combination of the time to see and actually slow down puts the total stopping distance at something like 20 metres.

Brakingdistances.com says you for a car @ 30kmh/20mph on a -12% gradient you shoud expect 6m of thinking, 14m of stopping. Which seems consistent.

Now imagine that incident happens once a "Kim Brigg's law" is passed: a pedestrian crosses the road, cyclist > 12m away, travelling at 18-20 mph. Cyclist sees pedestrian, shouts out. Tries to veer to the side, hits the child instead. That would appear to be enough to get the mini roundabout reinstated as Bristol's Public Gallows, and your eviscerated remains left to hang for days as school parents block the roundabout in their Volvo XC90s. "Look at that cyclist, he deserved it. Now, why is this anti-car council stopping me from driving at 30, can't they see I'm late for school?"

Who is to blame here?

It's not the kid's fault he wanted to be with his friends, it's not his fault all the parked cars made him invisible until he ran out.

He didn't look. Maybe he was enthusiastic about wanting to be with his friends. Maybe he listened for a car, but didn't hear any engine, so carried on out. Children are like that: Enthusiasm is not a crime.

What did the cyclist do wrong? Well, that's a question. Is freewheeling down a hill at 18-20 mph speed limit "reckless"? "careless"? Wilful endangerment of themselves and others? The Crown Prosecution would probably argue that, while everyone from the Daily Mail to the BBC would use verbs like "plowed" and "flew" as they covered the trial. In which case: driving round the area at 20 mph, especially in a low-engine-noise vehicle (hybrid, electric) is probably even more wilful.

The one thing you can point to the cyclist and say is: you knew term time had just started, and there were other kids on the pavement. Therefore it was likely there'd be more chidren ahead. So maybe you should have braked all the way down that hill. But: no matter what speed you go down that hill on a bike. if there is a car going the same way, it'll be right behind you or trying to get past.

Which moves to a more controversial question: is 20 mph too high a speed during school start/finish times? Should we drop from 20 mph to 15 in areas near schools? For everyone, drivers and cyclists alike?

Stopping distance experiments part 1

The Charlie Allinston case has not only raised the issue that fixed wheel, chain-only-braking bikes seem unsuited for the urban environment, but that cyclists themselves are criminals.

This was shown by a Met office video demonstrating how a mountain bike could stop in three metres, while a fixed wheel bike took 12 metres. Which, from the public video, looks pretty dubious.

Ignoring the thinking distance aspect of the problem (to be covered another time), neither of those bikes appear to be doing 18 mph. Martin Porter asserts that with a maximum deceleration force of a bike of 0.3g before the rider goes over the front bars, any bike is slower to decelerate than a car (max force 0.5g). We don't know the exact values. What we do know from experience is

• It's the front brake which does most of the conversion of kinetic energy into heat
• As you brake, you go forwards
• The back wheel, without weight, goes into a skid
• And it always seems to happen faster on tyres with less contact area (narrow tyres, knobbly mountain bike tyres on tarmac, ...)

Mountain bikers will know that to avoid going over the bars on a hard brake or steep descent means sticking your bum out the back, which is partly why dropper posts are so popular: lower C of G, better control on the descent.

Returning to the Allinston case, the police stated that Charlie had 6.5m to stop, and that because a mountain bike could have stopped in 3, his removal of the front brake made him culpable. But: they haven't show the actual CCTV of of the collision, so we don't know exactly what happened

What we can do though, is do the experiment proposed by the People's Cycling Front of South Gloucestershire: try to stop from 18 mph in under two car lengths.

Here then is our summary:

1. an experienced road and mountain biker cannot stop a road bike with touring tyres in the distance of two parked cars and a 1m gap between them. 
2. You can bring the speed down to about 6.5-7.5 mph (update: see the bottom of the post)

Equipment: a team road bike, "roadkill", purchased for $800 in 2000 somewhere in Oregon, a US state which is now charging people a tax for doing so.

• Tyres: Continental Top Contact 700x28 touring tyres, tyres which focus on all weather control and braking over rolling resistance and speed. That is: their braking should be as good as you can expect from any road tyre of a similar diameter.
• brakes: front and rear Shimano 105 rim brakes (from 2000), cables redone 24 months ago, pads Shimano 105/Dura-ace/Ultegra inserts
• Wheels: Mavic rims, hope hubs, again 24 months old and no rim wear.
• Garmin bike computer to determine speed from the GPS constellation and display speed as part of preparation for braking

Overall then: the brakes and tyres aren't going to degrade performance compared to any other road bikes with rim brakes.

Experiment:

1. Flat, traffic free road with enough visibility of the southern sky that GPS signal will work (Trivia: US Navstar satellites never orbit  > 54 degrees north or south, so above the lake district getting a signal is harder; for Galileo details ask one of our local engineers)
2. Two family cars, a "normal" gap between them (nobody had problems fitting today).
3. Turn on the Garmin to record speeds.
4. From a distance down the road, bring bike up to 18 mph & then coast briefly.
5. As you reach the front of the first car, brake as hard as you can safely, arse out the back and down as learned over the years on the MTB.
6. At end of the two car lengths, see what your exit speed is.
7. Repeat a few times.

Not the most rigorous, but with speed numbers coming from 31 orbiting atomic clocks it's as good on the flat as anything else.

Results

1. Getting to 18 mph on the flat does actually require effort, if attempted over a short distance. (This may make cyclists reluctant to shed that speed)
2. Even with warning and planning, you can't stop a bike in 2.5 car lengths from 18 mph
3. You can get down to 6.5-7.5 mph

Conclusions

1. If the met police video released to the media was the one used in court, then the qualify of the experiment has to be contested.
2. As well as the choice of the reference "not a fixie bike" as a mountain/hybrid bike with what appears to be wide surface area road tyres, its not clear that they are doing 18 mph when they get to the marker points where deceleration is meant to commence.
3. If someone else can stop from 18 mph to 0 mph in 3 metres, we'd love to see it.
4. Given warning, you can get to 6-7 mph, which may lead to reduce risk/scope of injury.
5. Given that cycle/pedestrian collisions at what for on road speeds are "low", we shouldn't be doing any cycle-paint-on-pavement bike paths, as they are engineering in danger

It'd be nice to see the logs of the police instrumentation data from their experiments. In fact, its something a defence lawyer should have been demanding: "show us the hard data"

Someone should run Bristol Bike Week event "can you stop in 6.5 metres with and without advance warning", to see what other people can do.

2017-09-11 Update : there's a flaw in the experiment: the measured exit speed is inevitably going to overestimate the actual one on any attempt to decellerate in a few metres.

Velocity (Speed) is distance/time: (d1 - d0) / t

But: what is the sampling interval of bike speedos (GPS and on-wheel?).

1. Not clear from GPS (though looking at the GPX file would probably show it), but 
2. on a 700x28 wheel the circumference is ~2.1 metres. 
3. Therefore the magnet on the wheel will only send packet to the bike computer every 2.1m of travel. 
4. Therefore the minimum distance which can be used to measure velocity is 2.1m. 
5. 18 mph is ~29 kmh
6. which is ~8 m/s
7. If you are trying to come to a halt  from 8 m/s n 6-8 metres then that's only four revolutions of the wheel, so every revolution will have to include a lot of deceleration: 
8. Assuming constant deceleration you are going have  to enter that final wheel rotation in travelling 1/4 of your entry velocity
9. so: it's inevitable that the distance travelled in that final rotation is going to be "something" between the entry velocity and the exit one
10. which is what the bike computer will end up displaying: it will overestimate the actual value

All we can really say is "the bike was still moving 10 m after attempting to decelerate from 8 m/s to 0 m/s"

How to do it better? Well:

1. you could let go of the brakes after crossing your chosen endpoint, coast for a few wheel lengths and so give the computer a constant velocity to measure. 
2. with the sub-cm resolution promised by Galileo's premium channels and a receiver set to sample many times a second, you could build a fully accurate model of decleration
3. you do rigorously measure the total distance travelled, assume constant deceleration over the distance and then work backwards from there to infer your velocity at the 6.5 metre mark

Anyway, it's mostly moot due to the thinking time even before you reach for the brake levers. Followup on that in the week, this time with video data. Essentially: you don't react fast enough.

WN15UKX beats the school run queues

It's term time in the city, a so the morning rush hour is worse, and we've seen the return of the mid-afternoon one, seen here.

In order to get anywhere, you need "flexible and imaginative solutions" as our Brexit negotiators say.


Here the driver of WN15UKX finds it impossible to make progress without risking their wing mirrors.

Residents of the inner city know that having wing mirrors is a sign of weakness, but here the driver of WN15 UKX isn't going to let the fact they value their bodywork slow them down. Instead, a neat little nip up onto the pavement, a quick sprint at 14 mph down the pavement and they are on their way. Maybe he was late for child pickup. Because you wouldn't want your child to walk home: it isn't safe, not even on the pavements.

Its drivers like this which give us selfish wanker BMW owners a bad reputation.