


The D.A.'s final report in the death of Brett Jarolimek (pdf), the second victim of Portland's black October '07, indicates the rider laid down a 36foot skid before colliding with the rightturning trash truck that tragically ran him over. Although maybe not as long as some people are visualizing, thirtysix feet is no joke. It indicates Jarolimek was moving at a pretty serious velocity at the point when he first reached for his brakes. Using the formula for gforce and observed values of gforce deceleration attainable by skilled riders, we can make some wildass guesses about just how fast he was moving. A skilled rider attempting to stop as quickly as possible will most likely initiate an involuntary reartire skid that is the natural byproduct of the type of front brake application that characterizes such a stop. This reartire skid will begin very shortly after the brakesqueezing begins, a split second, so to speak; the length of the skid can be assumed to be a few feet shorter than the total braking distance in a normal 'panic stop.' (In the shortest controlled stops by the best riders, the rear wheel comes off completely for the last 5 10 feet before stopping and obviously leaves no mark.) Calculating precise stopping distance (and thus initial velocity) in the Jarolimek incident is impossible because we don't know how fast he still may have been moving when his skidmark ended. If we assume he was almost but not quite able to slow to a stop at impact we can estimate his total stopping distance (minus reaction time) at about 42 feet or so. Gforce = (velocity)^2 X (.0333/stopping distance) I have observed with confidence that skilled riders can pull off .85 .89g stops. That's on level ground of course. That's a pretty serious deceleration, involving an exaggerated athletic body movement, and with the rear tire skipping along and wanting to come off the ground. In contrast, a .7 g stop is hohum, and I think easily attainable by almost everyone who rides a bike in minimal working order.[1] Anything less than that would be just plain easy. I think it's safe to say that Jarolimek, an experienced racer fighting for his life, was on his way to a .8 g stop or shorter, even on a slight downhill slope. (This is of course an assumption based on available information; it's possible that there were unknown unknowns that didn't come out in the report  extenuating circumstances again. For instance, maybe he was carrying something which prevented him from properly squeezing the front brake at all.) If we plug our estimated 42foot stopping distance into the formula with a .8g deceleration we come up with an initial velocity of about 32 mph. Now, I'm a believer that riders can do much better than that .8, and if he did then his initial velocity would have to have been even higher. The police estimate that Jarolimek was moving at a maximum of 28 mph doesn't seem to jibe with the formula, the length of the skid, and observed ability of skilled riders to stop their bikes in a certain distance. Essentially the police are claiming that this guy, an experienced rider in an absolute emergency, could only manage a .62  .72g casual LandRiderstyle deceleration. This could be a correct estimate, but only, in my opinion, if the skidmark lies on a downhill slope. I know there was a long downhill section of this road prior to the intersection, but I don't know exactly how much slope is at the intersection itself, where the skid took place (that's the problem with armchairing and pontificating from afar), and that's the relevant variable. The language of the report is ambiguous on this detail  they speak of a 7.5 % grade but it is unclear if they are talking about the terrain at the spot itself or the terrain leading up to it. I think it's possible that the surface was pointed downward enough here to make the police estimate jibe with the formula. In which case this entire diatribe of mine is moot, but that's never stopped me before. In the end it doesn't matter how fast he was going. All that matters is that he's dead, and it sucks. Sure this poor guy made some mistakes out there, but who hasn't? He didn't deserve what he got. Few, I imagine, deserve to die beneath a trash truck. I'm generally not one to focus on fatalities like this, and I hope to close this chapter and move on. Focusing on fatalities all the time in the typical fashion of safety ninnies everywhere can spread the misconception among already skittish beginning cyclists and the general public that bicycling is an activity that commonly ends in death for its participants. Of course, nothing could be further from the truth. And not only that, focusing on fatalities is a costly diversion away from where the statistically significant danger of cycling really lies  injuries. So focusing on fatalities screws up our perceptions on multiple levels, and leads us to do silly things. Maybe, if we're lucky, it will also give those of us who don't already have it a healthy respect for trash trucks and other monsters. [1] See the formulations of Joe Riel, who calculates that an .83g stop is possible simply by hanging one's weight off the back of the seat. He also shows how slope effects the formula (pdf). 


