30kmh – making streets liveable

snibgo
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Re: 30kmh – making streets liveable

Postby snibgo » 21 May 2013, 6:07pm

I (humbly) agree with CJ about the energy.

However, a factor sometimes overlooked is maximum power available. A cyclist who isn't strong (has a low maximum power) and needs to get up a fairly short hill may find it easier to accelerate before starting the hill. Although this requires more energy (to overcome increased air resistance), the energy is released over a prolonged period so the peak power required may be less than required for starting the hill at a slower speed.

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CJ
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Re: 30kmh – making streets liveable

Postby CJ » 22 May 2013, 10:00am

snibgo wrote:A cyclist who isn't strong (has a low maximum power) and needs to get up a fairly short hill may find it easier to accelerate before starting the hill. Although this requires more energy (to overcome increased air resistance), the energy is released over a prolonged period so the peak power required may be less than required for starting the hill at a slower speed.

Acknowledged, but only if he has not equipped his bicycle with a low enough gear to climb any gradient as slowly as may be necessary within his capabilities, or if he also lacks the skill to balance a bicycle at such a low speed.
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karlt
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Re: 30kmh – making streets liveable

Postby karlt » 22 May 2013, 10:40am

CJ wrote:
snibgo wrote:A cyclist who isn't strong (has a low maximum power) and needs to get up a fairly short hill may find it easier to accelerate before starting the hill. Although this requires more energy (to overcome increased air resistance), the energy is released over a prolonged period so the peak power required may be less than required for starting the hill at a slower speed.

Acknowledged, but only if he has not equipped his bicycle with a low enough gear to climb any gradient as slowly as may be necessary within his capabilities, or if he also lacks the skill to balance a bicycle at such a low speed.


Since it's relatively easy to balance down to around 1.5mph, can I suggest that the obvious action on dropping to such a speed is to get off and push?

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meic
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Re: 30kmh – making streets liveable

Postby meic » 22 May 2013, 11:03am

Since it's relatively easy to balance down to around 1.5mph


Not when your front wheel is lifting off the ground on every stroke, you have to keep to the 18" strip free of gravel and your back wheel is slipping.
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karlt
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Re: 30kmh – making streets liveable

Postby karlt » 22 May 2013, 11:29am

meic wrote:
Since it's relatively easy to balance down to around 1.5mph


Not when your front wheel is lifting off the ground on every stroke, you have to keep to the 18" strip free of gravel and your back wheel is slipping.


At which point you're definitely in walking territory.

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orbiter
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Re: 30kmh – making streets liveable

Postby orbiter » 22 May 2013, 10:04pm

patricktaylor wrote:
Vorpal wrote:... It clearly works in Norway ... It is not just wishful thinking ... the approximately 4 times as many journeys by bicycle made in Norway versus the UK (despite hills and winter weather) are not anecdotal.

I'm not doubting what happens in Norway. I'm asking for evidence it works, or would work, in the UK, and what kind of journeys by bicycle we are talking about (from cul-de-sac conversions) that would otherwise be in cars.

In Holland and Belgium as well as Norway, making residential streets cul-de-sacs works. Through traffic stops, naturally, so kids play on the street on their bikes and the adults party on it when the weather's good. Happens in the UK in existing cul-de-sacs.

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CJ
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Re: 30kmh – making streets liveable

Postby CJ » 23 May 2013, 10:52am

Firstly, I'm glad to see we've returned to topic and apologise for the diversion I caused.
patricktaylor wrote:I'm not doubting what happens in Norway. I'm asking for evidence it works, or would work, in the UK...

I think Norway makes a very good exemplar. Nobody can say it's irrelevant on account of being flatter, or kinder weather for cycling, or shorter distances between places, than any part of UK - even Scotland.
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Brucey
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Re: 30kmh – making streets liveable

Postby Brucey » 23 May 2013, 12:02pm

FWIW my personal suspicion is that;

a) pollution will be worse, not better, with a mandated 20mph speed limit.
b) people won't stick to it anyway.
c) the percieved 'safety' of 20mph motoring may well encourage drivers to indulge in even more dangerous behaviour behind the wheel, typically wotsiting about with their wotsiting phones...

We have had trial 20mph limits in the city where I live for a couple of years and I don't think that many people actually slow down in them. I live on a road with schools both on it and nearby; it also happens to be a short cut which avoids some traffic lights, and we regularly see people doing 50mph past parked cars etc. It is a miracle that no-one has been killed.

People cause accidents, and people take risks (knowingly or unknowingly) in relation to the perception of danger; quite how all this will pan out is anybody's guess.

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kwackers
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Re: 30kmh – making streets liveable

Postby kwackers » 23 May 2013, 12:14pm

Brucey wrote:a) pollution will be worse, not better, with a mandated 20mph speed limit.
b) people won't stick to it anyway.
c) the percieved 'safety' of 20mph motoring may well encourage drivers to indulge in even more dangerous behaviour behind the wheel, typically wotsiting about with their wotsiting phones...

If b then not a. (If people don't do it then it'll have no effect on pollution)

If b then not c. (You'll only feel safer if you're actually doing 20, plus if people actually did 20 then you'd need to significantly increase the number of collisions to have the same impact in terms of KSI's compared to the current 35-45 mph most do)

Mark1978
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Re: 30kmh – making streets liveable

Postby Mark1978 » 23 May 2013, 12:22pm

There have been many studies that people act (and drive) according to risk levels, they will keep risk levels down, of course, but the converse is that they drive to keep risk up to an acceptable level too. Therefore if you slap a 20mph on a wide open road, few will keep to it because the perceived risk is too low.

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horizon
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Re: 30kmh – making streets liveable

Postby horizon » 23 May 2013, 12:37pm

I don't wish to distract from this thread but the complaints of motorists leave me cold when I consider the equivalent treatment meted out to cyclists throughout the country and which is considered normal.

In town after town (probably almost every town in the UK in fact), there are streets where cyclists are restricted to 3 mph. In fact, cyclists are further inconvenienced by having to dismount in order to demonstrate that they are going no faster than 3 mph - no sitting on the bicycle at 3 mph! These are not minor back streets but the major roads through towns, often involving substantial stretches of road. The law is strictly enforced (I myself have been stopped by two policemen with booking sheets at the ready). This is considered absolutely normal: the law is there to protect motorists from mild inconvenience while proceeding on foot from their car park to a shop. Those same motorists will then return to their local streets to terrorize their neighbourhood and complain of being restricted to 20 mph. There are streets here in Cornwall where even cycling might be considered inconsiderate but there exist no speed restrictions of any kind apart from the usual 30 mph.

I'm sorry, but until drivers are asked to get out and push, I've no sympathy for them.
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orbiter
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Re: 30kmh – making streets liveable

Postby orbiter » 23 May 2013, 1:26pm

Brucey wrote:a) pollution will be worse, not better, with a mandated 20mph speed limit.
b) people won't stick to it anyway.
c) the percieved 'safety' of 20mph motoring may well encourage drivers to indulge in even more dangerous behaviour behind the wheel, typically wotsiting about with their wotsiting phones...


In practice, where there are 'self-enforcing' devices like chicanes, speed-tables or just large plant-pots in the road, most people do drive slower - or better still avoid the road altogether. Even cheaper & simpler if a through-road road is closed to cars with a couple of posts, the speed limit is almost irrelevant. This is being done in many central London 'rat-race' streets to improve cycling and life for the residents.

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Re: 30kmh – making streets liveable

Postby Brucey » 23 May 2013, 2:05pm

I think I should clarify; I think the least likely thing is that everyone in a car will drive at a steady 20mph whilst paying good attention to what is going on around them. I think that various people will do some (or all, at different times and places) of the things I have suggested.

It seems to me that this is what they do in a 30mph zone at present, pretty much, and in a 20mph zone they will be liable to do the same things but in an even more exaggerated fashion.

BTW I have nearly been knocked off my bike several times whilst negotiating various 'traffic calming' measures.

People in general (and motorists in particular) are not entirely rational and measures of this sort always have unintended consequences.

I refer anyone who hasn't seen it to a (Disney?) cartoon depicting the behaviour of 'Mr Walker' and 'Mr Driver' in a Jekyll and Hyde pastische. It was (I think) made in the 1940s (or 1930s even) but it still rings true today.

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Mark1978
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Re: 30kmh – making streets liveable

Postby Mark1978 » 23 May 2013, 2:20pm

Traffic calming measures are very very bad for cyclists, I can't really think of anything that makes my life easier.

One of the best ways to slow traffic down is increase the subjective risk, that can often be done by narrowing the carriageway, often this is done by putting in a centre hatching, which doesn't help as it seperates the flows, better to narrow the carriageway from either side and put in good wide cycle lanes.

e.g. This road http://goo.gl/maps/M6sIu really wide (former Great North Road) plenty of room for wide cycle lanes but they install crappy narrow useless things and give motor traffic more space than it actually needs.

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orbiter
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Re: 30kmh – making streets liveable

Postby orbiter » 23 May 2013, 2:26pm

Brucey wrote:BTW I have nearly been knocked off my bike several times whilst negotiating various 'traffic calming' measures.

Hard to comment but I haven't. Perhaps they were the wrong type in the wrong place.

.... measures of this sort always have unintended consequences.


Sweeping generalisation and just not so! Come to Holland/Belgium/... anywhere but Britain and see them working fine. Tables like this slow the traffic and don't impede bikes. It's not the people who are difererent but the whole infrastructure which encourages drivers (mostly) to drive carefully in residential streets