Impact of Luas Cross City

tomasrojo · 27-07-2017 11:52pm

OleRodrigo wrote: »

Those numbers are nonsense. Tired cyclist? What does that event mean.

You know sometimes you aren't as fresh as a daisy? That's a state humans call "tired".

OleRodrigo wrote: »

I braked hard last week at about 25 kmph and stopped after 1 to 2 m.

I think you either don't know what 25km/h is, or what 1m is. Or both.

ford2600 · 28-07-2017 7:52am

Stopping from 25km/h in 2m would require a friction factor of 1.27; an experienced cyclist can obtain a friction factor of about 0.95, assuming controlled use of both brakes, good weight distribution etc.(this is an in control no panic guy/girl)

At 0.95 ff the braking distance would be 2.58m to a stop from 25km/h. (assuming dry road surface, decent PSV of asphalt)

That is only the braking distance, the time it takes to react will vary, again with and experienced alert user significantly outperforming your typical Dublin bike cyclist. Reaction time includes the time taken to perceive the danger and the physical time required to apply the brakes.
The range here is typically 0.5 sec to 1.0.

The total stopping distance from 25km/h for a super alert, experienced cyclist
is 3.5m + 2.58m= 6.08m

Using 1 sec reaction time and .75 ff will give you 10.5m which is I assume what cyclecraft used.

The friction factor available between any given tire and any give surface will vary depending on speed.

Max grip between a tire and surface is at about 20 percent of tire slip, you have 100 percent at lockup.

schemingbohemia · 28-07-2017 9:44am

ford2600 wrote: »

Stopping from 25km/h in 2m would require a friction factor of 1.27; an experienced cyclist can obtain a friction factor of about 0.95, assuming controlled use of both brakes, good weight distribution etc.(this is an in control no panic guy/girl)

At 0.95 ff the braking distance would be 2.58m to a stop from 25km/h. (assuming dry road surface, decent PSV of asphalt)

That is only the braking distance, the time it takes to react will vary, again with and experienced alert user significantly outperforming your typical Dublin bike cyclist. Reaction time includes the time taken to perceive the danger and the physical time required to apply the brakes.
The range here is typically 0.5 sec to 1.0.

The total stopping distance from 25km/h for a super alert, experienced cyclist
is 3.5m + 2.58m= 6.08m

Using 1 sec reaction time and .75 ff will give you 10.5m which is I assume what cyclecraft used.

The friction factor available between any given tire and any give surface will vary depending on speed.

Max grip between a tire and surface is at about 20 percent of tire slip, you have 100 percent at lockup.

Yeah but they're just like facts and science and stuff, sure everyone knows that this is all about emotion....

magicbastarder · 28-07-2017 9:56am

maybe by '1 to 2 m' he meant '1 to 2 miles' - he didn't explicitly say it was a bike he was on, maybe it was a ship.

OleRodrigo · 28-07-2017 10:21am

maybe... maybe ..it was 2.5

Mr. Grieves · 28-07-2017 10:24am

Does anyone else think a braking distance competition would be good craic? I'm tempted to do a comparison between a few of my bikes.

OleRodrigo · 28-07-2017 10:37am

Its a moot point anyway. At the various points of contention, all traffic will be moving slow.

ford2600 · 28-07-2017 11:01am

OleRodrigo wrote: »

maybe... maybe ..it was 2.5

Bet you spilt the latte to...

bazermc · 28-07-2017 12:56pm

Well lads. The advert, and its incorrect information has annoyed me so much I have made a complaint to the Advertising standards agency. I'll let ye know how I get on.

OleRodrigo · 28-07-2017 1:24pm

ford2600 wrote: »

Bet you spilt the latte to...

wasn't the same day your honour, but yes, even I couldn't have kept it intact that day

OleRodrigo · 28-07-2017 1:38pm

bazermc wrote: »

Well lads. The advert, and its incorrect information has annoyed me so much I have made a complaint to the Advertising standards agency. I'll let ye know how I get on.

Have you considered calling Joe? Such an outrage deserves no less!

Mr. Grieves · 28-07-2017 1:41pm

Ok, I did a little test on my lunch break:

Flat road, dry tarmac, slight headwind.
Rider + bike = 78 kg
Brakes: hydraulic discs with 180mm rotors front, 160mm rear
Tyres: 29er, 2.3" wide, approx 20 psi

At 30 km/hr, on my 5th attempt, I manged to stop in 4 m. It took a little practice, my first attempt was 7 m. You need to throw your weight backwards and even still the back wheel is lifting.

I don't think you would get a much better setup in terms of brakes/grip, but further practice would give further improvements, I think.

Of course reaction time is not included as I was anticipating the line on the road where I would start braking.

I may repeat this on the road bike in the wet to get a 'worst-case' number.

flatface · 28-07-2017 2:30pm

I know from painful experience that I emergency brake slower than a taxi. I try to keep more distance now but car brakes are more effective IMO

Mr. Grieves · 28-07-2017 2:36pm

flatface wrote: »

I know from painful experience that I emergency brake slower than a taxi. I try to keep more distance now but car brakes are more effective IMO

Hence the username? :P

ford2600 · 28-07-2017 3:27pm

Mr. Grieves wrote: »

Ok, I did a little test on my lunch break:

Flat road, dry tarmac, slight headwind.
Rider + bike = 78 kg
Brakes: hydraulic discs with 180mm rotors front, 160mm rear
Tyres: 29er, 2.3" wide, approx 20 psi

At 30 km/hr, on my 5th attempt, I manged to stop in 4 m. It took a little practice, my first attempt was 7 m. You need to throw your weight backwards and even still the back wheel is lifting.

I don't think you would get a much better setup in terms of brakes/grip, but further practice would give further improvements, I think.

Of course reaction time is not included as I was anticipating the line on the road where I would start braking.

I may repeat this on the road bike in the wet to get a 'worst-case' number.

Friction factor of 0.884, which is pretty decent.

Really hard to get to 0.95; where you doing a manual abs or had you full lockup?

Mr. Grieves · 28-07-2017 4:09pm

Front didn't lock (but according to your graph must have been slipping to some degree), back did but it was lifting off the ground anyway. I guess if I got my weight further back the front would lock too.

There's probably a few large sources of error in my measurement, the biggest being the exact location where I first applied the brakes. A slo-mo video would probably be useful for recording that.

Mr. Grieves · 28-07-2017 4:17pm

ford2600 wrote: »

Friction factor of 0.884, which is pretty decent.

How do you calculate this?

ford2600 · 28-07-2017 4:25pm

Mr. Grieves wrote: »

How do you calculate this?

On phone so forgive notation.

For where vehicle brakes to a stop

Initial velocity squared = 2.(f)(g)(d)

Where f is dimensionless friction factor
g iso gravitational constant 9.81
d is skid distance

Velocity is in m/s BTW!

papu · 28-07-2017 4:49pm

ford2600 wrote: »

On phone so forgive notation.

For where vehicle brakes to a stop

Initial velocity squared = 2.(f)(g)(d)

Where f is dimensionless friction factor
g iso gravitational constant 9.81
d is skid distance

Velocity is in m/s BTW!

Here is a calculator and background

http://hyperphysics.phy-astr.gsu.edu/hbase/crstp.html

OleRodrigo · 28-07-2017 8:30pm

So the Luas travels at around 20 kmph around junctions with pedestrians and vehicles. We can assume it will continue to do so around the contentious junctions of the Cross City extension.

Bikes have an average speed of 12 kmph, but lets say a median speed of 17 kmph in the city center.

What have the stopping distances mentioned got to do with anything, in this context ?

tomasrojo · 29-07-2017 5:07pm

Sticky bottle has an article about how often people on bikes make the Luas do emergency stops. Not all that often, all things considered.
http://www.stickybottle.com/latest-news/luas-reveals-number-incidents-cyclists-drivers-pedestrians/

papu · 29-07-2017 6:07pm

tomasrojo wrote: »

Sticky bottle has an article about how often people on bikes make the Luas do emergency stops. Not all that often, all things considered.
http://www.stickybottle.com/latest-news/luas-reveals-number-incidents-cyclists-drivers-pedestrians/

That's a good write up, the messages between the three campaigns have been very much skewed against the least hazardous and dangerous mode of transport. If they really wanted to combat luas collisions, hold ups and emergency brakes they would continually run sponsored advertisement for motorists.

OleRodrigo · 29-07-2017 6:45pm

All things considered, its what you might expect. Cyclists are a small portion of traffic in the city center, compared with vehicles and pedestrians, including at points of intersection with the Luas.

I'd bet their percentage of incidents is broadly in line with their population percentage.

magicbastarder · 29-07-2017 9:07pm

so is it just me who didn't really see a fault with the video?
they tackled the three main categories of road user who might interact with the luas. what's the implication - that because cyclists are the third most likely to be hit, that it shouldn't be addressed?

papu · 29-07-2017 9:31pm

magicbastarder wrote: »

so is it just me who didn't really see a fault with the video?
they tackled the three main categories of road user who might interact with the luas. what's the implication - that because cyclists are the third most likely to be hit, that it shouldn't be addressed?

Did you read the article?

tomasrojo · 30-07-2017 12:28pm

tomasrojo wrote: »

Funnily enough, cycling is more important, not just than the Luas, but than rail in total, according to recent data. 50% higher modal share.
https://twitter.com/HanneyDP/status/881529097666654209

That's nationally. Not sure what restricting focus to Dublin would do: both rail and cycling would be a bigger proportion.

Well, I need wonder no longer. More people carried by bike than rail in Dublin.

Census 2016 results show that that 54,009 people put cycling down as their main mode of transport to work and education, while 50,970 people use Luas, Dart, and Commuter Rail.
Those cycling amount to 7.1% of residents commuters, while all types of rail commuters account for 6.7%.

http://irishcycle.com/2017/07/30/more-residents-commute-by-bicycle-than-by-luas-and-dart-in-dublin-city-and-suburbs/

Feckofff · 30-07-2017 12:47pm

What width tyre would you need to be safe on the tracks?

I'm thinking of throwing a fat tyre on the front just to stop supermaning over the handle bars.

ED E · 30-07-2017 12:54pm

Cant find the spec, its 1435mm (Standard Gauge) but thats the internal measurement.

At a guess 45mm+ would be ok. They're still slippy c*nts though.

Arcade_Tryer · 30-07-2017 1:35pm

Or you could slow down and turn your handlebars toward a right angle when crossing the tracks? You'll lose momentum and it will lead to an increased journey time, but you won't fall.

ED E · 30-07-2017 2:30pm

Arcade_Tryer wrote: »

Or you could slow down and turn your handlebars toward a right angle when crossing the tracks? You'll lose momentum and it will lead to an increased journey time, but you won't fall.

Try that in three columns of traffic with a Dublin Bus on your heel and let us know how you get on.

Safe crossings are not possible due to the failure of a design.

Impact of Luas Cross City

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