Hitting a pedestrian

[jarlrmai]

I avoided a woman who stepped (pretty much jogged) out further into the road from behind a van parked on the roadside, this was down a slight decline and I was doing around 20, I avoided her mainly because I was riding in a very primary position out of the door zone, pretty much by the white line, I still had to warn her, brake sharply and swerve slightly to avoid her.

The closest i've had is a jogger step from the pavement into the road, I presume to avoid something on the pavement, I was right alongside him at the time, now I treat all joggers as if they are going to do this.

 

[theclaud]

v^2 = u^2 + 2as
0 = 8.9*8.9 +2a*6
a = - (8.9*8.9) / 12
a = -6.6

6.6 m/s^2 is about 0.7g. Please check my working becuase I haven't

I've not much idea what this means but I intend to "like" it anyway, on trust.

 

[w00hoo_kent]

now I treat all joggers as if they are going to do this.

Never trust a jogger, they're the ones that always find the bodies.

You have to treat opaque vehicles as you would anything else you can't see through. You can get a bit of a hint by looking low, you sometimes see the legs, but really give them space, or pass them slow if you don't want to end up hitting someone one day.

 

[Dan B]

What factor does mass play versus speed?

None at all, for that particular calculation. Mass might play a part in calculating the maximum possible deceleration (perhaps a heavier vehicle grips the road better, for example) and will certainly be related to how much damage you do if you don't stop in the space available, but the question posed was merely "how hard would you have to brake to stop in 6 metres" not "is that even possible on a bike".

For the record http://www.bikeforums.net/bicycle-m...ing-road-bike-braking-power.html#post10349193 suggests that the answer to the latter question is "yes, sometimes, if you're good at it"

 

[Markymark]

But surely that's just the deceleration, nothing to do with the force? Anything changing from velocity to rest will have the same acceleration (deceleration in this case). 6.6 m/s/s means nothing in the context of a feather as oppsoed to a bowling ball

The point, I thought, is about the force required to stop and that is directly linked to mass with F=ma. You have calculated the acceleration, but to get the force (ie how hard to brake), you'll need the mass too.

 

[.stu]

And your speed played no part in getting you and your bike to the point where you were far too close to stop at that particular point in time. I see.

Oh ffs quit your trolling please.

I did not hit the old man, nor was I riding dangerously or recklessly - the fact of the matter was that he did something unpredictable, and I only mentioned it because I wanted to highlight the fact that pedestrians can do things that cause collisions with other road users, and for which they are solely responsible. However, you, who who not there, seem to find fault in my riding ability no matter what I say. Does that make you feel big?

 

[KneesUp]

Oh ffs quit your trolling please.

I did not hit the old man, nor was I riding dangerously or recklessly - the fact of the matter was that he did something unpredictable, and I only mentioned it because I wanted to highlight the fact that pedestrians can do things that cause collisions with other road users, and for which they are solely responsible. However, you, who who not there, seem to find fault in my riding ability no matter what I say. Does that make you feel big?

@GrumpyGregry gets confused. He holds that the more kinetic energy you in control of, the more care you must take - which is a reasonable rule of thumb. Unfortunately he seems to extend this to suggest that all accidents are caused by the rider/driver/thing with most kinetic energy not paying attention, and therefore the fault is always with the thing with most kinetic energy. Although of course we don't know which had the more kinetic energy in the original situation - a light cyclist on a light bike might easily have less kinetic energy than a fat person running, for example.

 

[KneesUp]

When someone is standing at a crossing and wanting to cross, their behaviour is highly predictable. They are extremely likely to cross the road at some point.

And very unlikely to do so in front of oncoming traffic. I think most of us would predict that they would wait, wouldn't we?

 

[cd365]

And very unlikely to do so in front of oncoming traffic. I think most of us would predict that they would wait, wouldn't we?

Not on this forum

 

[Markymark]

A fast bike can have greater KE than a small car going slowly around a corner.

 

[KneesUp]

In the example given, that was the prediction. It turned out not quite right.

That's in the nature of predicting the behaviour of living things we don't control, though.

 

[theclaud]

And very unlikely to do so in front of oncoming traffic. I think most of us would predict that they would wait, wouldn't we?

Seeing as almost everyone has umpteen stories about pedestrians doing very similar "unpredictable" things, you would imagine that we would adjust the way we make predictions, rather than hope that people's behaviour will adjust to fit our faulty ones.

 

[KneesUp]

Seeing as almost everyone has umpteen stories about pedestrians doing very similar "unpredictable" things, you would imagine that we would adjust the way we make predictions, rather than hope that people's behaviour will adjust to fit our faulty ones.

The vast majority of pedestrians do not walk out in front of people. It would be a dull forum if we told each other about it though.

 

[Markymark]

Expect the unexpected.

I expect some sort of Spanish Inquisition over that.

 

[theclaud]

The vast majority of pedestrians do not walk out in front of people. It would be a dull forum if we told each other about it though.

Do you live in Sweden?