Thursday, 21 September 2017

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?

Sunday, 10 September 2017

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.

Thursday, 7 September 2017

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.

Monday, 15 May 2017

The Centre: East to West: From Mediocre to Dangerous

Following on from our trip across The Centre from West to East, here is the west to east experience.

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Heading up Queen Charlotte Street from Queens Square, we first get to see a near-collision between a deliveroo rider and a small child running out from the side. It's possible to conclude the rider doesn't have a small child, or they'd have known that trying to control one is futile: asking the parent to do so even more so. "Fuck off you wanker" is the correct response here.

Then it's left onto the half-of-Baldwin Street path. A lot of people accuse Ferguson of following some anti-car, pro bicycle policy. Well, this is the main legacy of his of his reign from a cycling perspective. London also had a mayor prepared to sacrifice the country in his ambition to become PM.

The Baldwin Street path starts of as a reference example of what modern thinking on segregated cycle routes should be: not just a safe separation from cars, but a clearly delineated separation from people on foot, the bikes not having to weave between people -better for all.

It then switches to being a reference example of what you expect to see in Bristol: the bike path suddenly gives up in order to have some car parking, before ending up at some lights. Here the other tax-dodger decides not to stop for the lights, so proving that we do show such events when they happen. Its notable that actually he had less to worry about across the junction than our reporter, what with the past-the-lights taxi and the van swerving over to pick up a mate.

On to Baldwin Street, and what do we see?

  • An explicitly cut out path to the lights +10
  • Some lights: 0
  • No clear indication of which bits of the lights your bike should go to: -10
  • Lights green when the road going straight on: +10
  • A central plaza where there is no indication whatsoever of where you are meant to go to cycle across to the other side; -10
  • Another set of lights with no clear cues as to which side a bike should be on: -10
  • The lights now red, so adding a delay of ten seconds: -5
  • Roadworks in the middle so not actually proving any way to cycle further: -20
  • Some pedestrian lights to wait for and use: +5
  • Signs of a bike path possibly appearing by the hippodrome: +10
  • The bike path not being ready to use:  -5
  • The need to execute (badly) a bunny-hop to get your bike up the kerb *where the road to Colston-the-Slaver-Hill used to be*-10
  • Another bit of utterly undelineated bike path: -10
  • The utterly undelinated bike path now abandoning you to a road where nobody expects bikes to come from: -20
Overall then: 35 points of good,  -25 points of work-in-progress points (the chaos, the bunny hop, the bike path. And -60 points of fundamental structural flaws. A mishmash of walk/cycle routes with artistic tiles providing now cues as to where a bike should go, so hard-coding conflict into the centre at the cost of some premium tiling.

This was done by someone who wants "an urban realm" design, despite the fact they've just added a new road and bus line through the heart of the area, someone who doesn't actually want bikes there and finds the idea of having a functional way to get across by bike unsightly. It is, to use a technical term, "bollocks".

the worst part is probably the approach to Colston Hill. Until recently, there was a road entrance there. All they had to add was a sign and some build out to narrow the entrance. Everything else was in place. Except they spent money on adding a new pavement and some tiles, and in doing so removed the option of a safe exit. Now all private vehicles on that road will be entering or exiting Pipe Lane: a road where the road signage has been changed so that Colston Street has lost the right of way it used to have. This is now dangerous.





Thursday, 4 May 2017

Don't worry Richard Eddy: there's still Colston Mini Mart

Cllr Richard Eddy is apparently refusing to visit Colston Hall, once it's no longer named after someone who'd be on trial for Crimes against Humanity were they to attempt the same business today.



Because yes, it's named after Bristol's most important slave trader, and it's something the city should recognise is an affront to the rest of the country. Naming a prestigious building after a slaver may have been considered socially acceptable in the Victorian era, but we've moved on: time for the city to. That includes the two Colston Schools, the various roads, an ugly 1970s tower block and other bloodstains round the city.

What the renaming has shown up is how controversial the topic still is: from polls in the evening post, to articles in the "foreign-interference in the UK election national press", condemning "political correctness" for this historical revisionism. Well, yes, celebrating slavery is considered "politically incorrect" these days.

It's interesting what it's thrown up through, not just the view of it as a left-wing/right-wing split, but it can also be seen as a Bristolian vs "newcomer" split, with "Bristolian, born and bred" being a code-phrase for "not from London". Well, it's easy for people to feel defensive, but really changing the name of the hall isn't an attack on Bristol, it's moving the city on. Or, as The Bristolian notes: nobody has ever cared about what happens to parts of the city that aren't associated with it rulers, be it schools across the city, the river the M32 was built over, or any bit of greenery that doesn't have the word "Clifton" in its title or address. For people who want to know a bit more about these topics, consider the Bristol Radical History group.

What about Richard Eddy? Is he going to suddenly discover that alongside the history of Bristol's elite, there's the history of Bristol's residents, from the miners of Bedminster to the striking bus drivers of 1960s St Pauls? Unlikely. Instead he's just chosen to be ever excluded from the building-formerly-known-as-Colston-Hall.

We have some good news here: Colston Mini Mart still stands strong against this wave of political correctness

People don't appreciate this, but Colston Mini Mart has an important role to play in the city. It is the nearest place to the Bristol Heart Institute where you can buy cigarettes. You don't appreciate this until you're stuck in there for a week, the same wrist band giving you a wifi password marking you out as someone the door staff won't let out. You're reduced to texting friends and family to visit, bringing up with them a double latte from Costa and a pack of silk cuts. Then you can sneak out after hours onto the balcony and have a quick cigarette while sharing anecdotes of heart bypasses. Nothing to smoke and the remains of your life may be longer, but it will be more painful.



That's what we all have to look forward too. All that we get to choose is: do we get anything from the Colston Mini Mark on the way out. Here then, Richard Eddy will be able to go out with the rest of the city.

Sunday, 23 April 2017

Metrobus Enhanced Centre: west to east

Apparently the Metrobus project will bring wonderful cycling facilities to the city.

We await this with curiosity.

We do know that
  • right now there is nothing
  • there is nothing on the travelwest web site about how to get across alive on a bicycle
  • the travelwest web site can't even get their "out of baldwin street for cars" map right.
Overall not a good sign.

Historically, the crossing which is blocked was a walk/cycle crossing where you could cycle randomly around until you made it over. This never actually glued up very well with baldwin street, on account of the railings and the oncoming traffic; you'd have to head over to the bit of the centre which was bus lane only, cycle over the ped crossings there, or go down the bus & bike bit of road the bus drivers felt were theirs. Or you stay on the ped/cycle inner bit, zig zag through people and children, creating the impression that cyclists were tax dodging criminals who cycled where they shouldn't. Yes, the evening post did an article on that topic a very long time ago.


So, we sent our expendable tax dodger to go west-east across the centre to see how things are today


Pretty awful at the start, mediocre in the middle, and just as bad as before at the end.

Awful at the start: well, what do you do? No signs, just a closed off crossing. Our tax dodger eventually went for the coned off lane in the middle and made their way to the new bit of the centre.


Mediocre at the middle. The one thing the Baldwin Street path gets right is: clearly delineated as a bike path. Tax dodgers stay on it, people don't walk down the middle (Except on friday nights, obviously), and people on the pavement don't have to worry about cyclists weaving through them because there's a f-obvious bike lane to use instead.

The new design has some faint tiles on the ground which may mean its a bike lane. Hard to tell. They don't currently join up with anything.

There's some new lights, possibly split into bike & ped, but with no cues, everyone just spread out. Watch out for the person nearly being hit by the turning bus: bit of a design flaw there, even if that's where the cyclists are meant to be.

Finally, at the end, just as bad as before. It does look like there might be some link off to the left, but again, it's been made out of artisanal tiles rather than useful roadbuilding materials, so who knows. You can avoid worrying about this by getting onto the bus zone, coming off it to get towards the Arnolfini.


Once you've actually crossed the centre, you can get down to the prince st bridge (walking), then on to bedminster. Why? Motaman is having a closing down sale! Bedminster's main shopping destination is being shut down as the building is being turned into flats! Gentrification is coming to Bemmy and it's not good.

Wednesday, 19 April 2017

Pavements cause pollution.

Known saboteur Redvee has a video up showing the taxi WR54KZX forced to drive on the pavement to turn left into Bridewell Street.



We say forced, as this is clearly due to the Metrobus roadworks going on further ahead on the road. Before Metrobus there were never any queues on the roads leading to the Centre, and so no need for taxis to drive on pavements in order to stop this city grinding to a halt. And, as this is a 2004 EURO3 Diesel taxi, the pollution from its engine is awful, even by the standards of the VW test rigging team. By driving up on the pavement, the Taxi reduced the amount of pollution the city experiences. This is why pavements cause pollution. No pavements: more lanes. No pavements: fewer people walking, no need for zebra crossings or pedestrian phases in lights. We must do more in our city to discourage walking —even more than the Metrobus works team are already doing for us.

One thing to consider though: the taxi did go up the blind spot of that bus. If the bus had turned left the taxi and its passengers could have been crushed.


We propose that every bus and lorry in the city should have a sign warning taxis not to drive up the inside of them to prevent such a calamity happening in future