Last time I checked, I only found a law that said a yellow light means "prepare for red." There are intersections on my commute with a five-second yellow and zero all-red time that take more than five seconds to cross, especially in a headwind, so I could find myself in a similar situation even if I had zero chance to stop for the yellow.

edit: paced them out on my way home. 150 feet to cross in 5 seconds.

If you run the equations, mass cancels out. Maximum deceleration on a bike is limited by where your center of mass is located relative to the front wheel. That said, still allow a generous fudge factor -- even if your hand was on the brake lever, reaction time is half a second, and maximum braking is not really practical.

Again, it seems obvious to me that as cyclists we have wherever we encounter them, and I believe we are legally accountable under the code if we do not.

If there is any confusion, let me state clearly that your video does not demonstrate
to me the exercise of due care for the safety of this pedestrian. Sorry, but that's
how it looks from where I sit. As to the guy who killed someone, I think he's lucky
the crowd did not tear him limb from limb.

I'd be curious to see how mass cancels out. If F=ma where F is the force to apply an acceleration of a to a mass of m it is clear that as m increases so does F. Unless a heavier rider has upgraded their brakes to take into account they are heavier the braking force available is based on the same brake block/braking surface combo regardless of the weight of the rider.

If the maximum safe braking force is capped by the desire to not go over the handlebars it may be that mass doesn't affect the calculation; if it's capped by how much deceleration the braking system can provide then it's harder to see how mass can do anything other than vary it.

This is why trains can stop in the same distance as cars.

One thing going on is that cars make a lot more noise and have a larger visual profile than a bicycle. So based on probably thousands of crossings of the street, a given pedestrian will know, based on sound and peripheral vision, that the cars are stopped and the way is clear. If they haven't had an encounter with a cyclist entering the intersection as the light turns, they simply aren't trained to look for him. I don't mean this as an excuse, merely an explanation.

I probably could have stopped had I applied the brakes as soon as the light turned yellow, however, as I was approaching the intersection, I saw a green light, I was then scanning the cross street, and the near-side crosswalk - not staring at the light as I approached the intersection. As I was about to enter the intersection I looked back up at the light, and it was yellow, at this point it was too late to stop. I do not disown all responsibility for this, however, I believe that for traffic, the law is that when the light turns green, you must wait for traffic in the intersection to clear before proceeding. I am not sure if there is a similar requirement for pedestrians, but common sense would suggest that it is not a good idea to step in front of a moving vehicle regardless of the color of the light. The fact that I was on a bicycle, which is slower and more maneuverable than a car probably kept the pedestrian from having a much worse experience - regardless of who might have been at fault.

There is. Read my posting of the VC

Nonetheless, read subsection d again........

the bottom line here is that if you hit a pedestrian in a crosswalk,
while operating a car or a bicycle, your subsequent life will be made
pretty unpleasant. A lot of guys might look at that fact, and possibly
modify their riding style. Some won't....it's a personal choice.

I cannot make you smarter, safer, or a better cyclist. But you have the
California VC sections that apply, FWIW.:thumb:

When it comes to braking, mass does indeed "cancel out" form the pure classic mechanic point of view. It is true that larger mass means larger inertia. But larger mass at the same time means larger friction (by the same factor). These two effect cancel themselves out precisely, which is why the classic mechanical formula for friction-limited stopping distance does not depend on mass at all

d = v^2 / 2gf

where 'v' is the initial speed, 'g' is acceleration due to gravity and 'f' is the friction coefficient. This formula means that under friction braking from the same initial speed, all bodies have exactly the same stopping distance, regardless of their mass.

However, in real life the considerations of mass redistribution under deceleration, shape of contact path and limitations of specific braking systems have significant effect on the braking distance. This is the reason why heavier cars cannot compete with smaller cars in therms of braking distance (albeit the gap is getting smaller and smaller as the braking technology improves).

In case of a bicycle this formula does not immediately work either, since bicycle braking is not friction-limited, but rather balance-limited: on a dry pavement a bicycle will flip over its front wheel well before it reaches its friction limit. Increasing the mass of the rider (a mass located relatively high, BTW) will shift the balance towards the flip even further.

You're right. I knew mass canceled in the friction-limited case, and thought that would also apply to the balance-limited case.

This is the formula for "minimum stopping distance". "Friction-limited case" means that you're able to brake/decelerate at a rate that's just short of the tires starting to skid - like you might see on an emergency car maneuver with ABS, perfect tires and perfect pavement.

The statement that started this discussion was that a heavy rider would have a greater ACTUAL braking distance than a featherweight rider. That'd be an interesting experiment - putting up skilled riders of different masses and equivalent equipment. But every one of them would be longer than the distance given by that calculator.

From Bob Mionske's column, in the comments:

I don't think that's true. The bicycle will not flip over the front wheel, unless the rider is going downhill or has his weight shifted far forward, over the handlebars. Assuming flat road and typical posture, in the friction limited case, we have two sources of torque: friction between the front wheel and the pavement, with torque m*r*f, where m is mass of the bicycle and the rider, r is the radius of the wheel, and f is friction; and gravity, with torque m*d, where d is horizontal distance between the front axle and the center of gravity of the bicycle and the rider. Under normal conditions, f<1 and d>r, which means that friction is insufficient to overcome gravity and to flip over the bicycle.

No offense intended, but your assumptions and your equations
do not reflect the realities....as any of the more adventurous
speedster bikers here can testify.

Check out the chapter in Bicycling Science on braking, for a better
modeling of what's actually going on when you brake.. .. there's a weight
shift to the front that happens automatically in braking a standard
configuration, upright, double diamond framed bicycle.

This is why the majority of your braking power is effectively applied
to the front, and why it's not that hard to endo........

You guys need to either experience this yourself or think about it some more. The "intergreen" period is only a few seconds (that is the time between when one direction has green and when the other section has green - both ways have a red light). The slower you are going on you bike, the worse this problem is. You can be riding along at say 5 mph and you go through a green light (yes green). But, before you get even half-way across that intersection the light goes orange then red. AND, if there are pedestrians on the crosswalk it becomes hazardous. Neither the pedestrians nor the rider are at fault because both of them entered the intersection with a green light.

So how do I know this? Because it happens to me every day on my commute. It's not a problem anymore because I know that at this particular intersection, I need to stop even though the light is green. The fault lies with the timing of the lights and one day I will write to the city admin and suggest they increase the intergreen time.

Having a bell on your bike is also helpful in cases like this.

Link (*.pdf) appears to be removed. Were you able to make a copy to your hard drive? if so would you be kind enough to share?

There are numerous links to the work on the interwebz.

Here's one http://www.2shared.com/document/BtZF...ience_PDF.html

but you really only need to look at the specific chapter on braking,
chapter 7, in particular the discussion on longitudinal stability while
braking. This starts on p243 in my edition of the book.

The rest of the chapter is very interesting, but less applicable.

No offense, and a lot of discussion of the vehicle code and physics formulae, but you should have stopped. Clearly. There's no way in heck I would have gone through that big an intersection with the light changing that far from going into the actual intersection. The ped did NOTHING wrong IMO, though they probably should have looked. It's a smart thing to have the camera even if you aren't using it to "be a hero" as the ads proclaim, but in this case, it showed that you were wrong. Just my opinion.

I was in SF Thursday and Friday. I rode all around that intersection. It looks like there is a block-long descent on Castro leading to Market Street, which means Bucchere must have been sprinting towards the intersection in order to reach 35 mph. That is nuts! In SF, even when I am descending a street where I don't have stop signs or traffic lights to watch out for, I always approach intersections with caution. It is just too congested and busy to take chances. That Market and Castro intersection is very busy, and I can't imagine entering it at any kind of speed, let alone 35 mph! :eek:

IMO the pedestrians in sauerwalds video were at fault. No laws were broken, and he did display caution (slowing, and then swerving to not hit them). The peds were fools for stepping into a street without looking. Sauerwalds did everything right. He's just not able to anticipate the inattentiveness of others.