Hypothesized mechanisms for “safety in numbers”

Safety in numbers is a cycling safety rule that says that the more people ride bikes, the safer each rider will be. Hypothesized mechanisms include (1) driver familiarity – because drivers more often see bikes on the road, they become better-trained to see them on the road and (2) driver empathy – because so many drivers also ride bikes, they are more aware-of/concerned-about bicycle safety issues. (Here’s a nice pile of pointers to papers, tracked down by a real live researcher.)

I think both of these mechanisms are entirely possible, but riding an actual bike in actual traffic in actual crowds of cyclists, I’ve noticed what looks like other ways that greater numbers provide safety. In at least one case I’ve captured it on video. The difference between these mechanisms and the others that are hypothesized is that they are extremely short term – “safety in numbers” can appear whenever there is a biking crowd and disappear as soon as it disperses. These are also somewhat more likely in crowded urban areas and depend somewhat on the existence of traffic jams.

The first mechanism I might call “schooling” (after Bike Snob’s “shoaling” and “salmoning”). Bikes riding in a line are schooling, and for several common cycling hazards, most of the risk is borne by the lead fish, and the rest get a free ride. If someone in a parked car is not looking for bikes and is about to open their door, but then a bike zips by, it’s not unreasonable that they would be startled, and maybe then look to see if it was clear – and if the bikes are schooling, all the followers get the benefit of that. The dooring risk is almost entirely on the lead cyclist. Similarly, cars pulling into or across traffic represent a threat only to the lead cyclist, and very little to the ones in the rear. A line of bikes is also somewhat protective against right hooks, since those usually occur when a driver thinks they can overtake a bike and turn right, or forgets the presence of a single bike. With a line of bikes, once the first is across the side street, it is obvious to the driver that a right turn is not possible.

A second method is less obvious, but safety decreases markedly in the range of speeds between the slowest and fastest typical commuters. A low-speed (below 10mph) crash is stupidly survivable; you can almost step off your bike as it falls down. A high-speed crash (above 20mph) is far more likely to send you to the hospital or worse. Bike lanes at rush hour tend to run single file for some distance, usually because the bikes are hemmed in between parked cars on the right and “parked” cars on the left. Inevitably, some riders will be slower than others, and the inability to pass then compels the would-be-faster riders behind to slow down until they can pass. This makes them safer, whether they like it or not. This, I’ve seen on video, where I play the role of impatient rider. The probability of this delay and the difficulty of passing both rise pretty quickly once there’s more than a couple of riders delayed behind a slow leader.

After dark, a school-of-fish also multiplies the effectiveness of any lights that cyclists might be using. Just considering use of lights and not, if an unlit cyclist pairs up with one using lights, they can obtain most of the safety benefit of the lights. When two cyclists both have lights, the variations in their movement or in the flashing style of their different lights will create additional visibility over a single cyclist; for example, one cyclist’s flashing light might draw attention, but the other’s steady light might allow a driver to accurately locate the pair. Not nearly as many cyclists ride at night, but bicycle lighting use in the US is not nearly as good as it should be, so there’s plenty of room for this to help.

I don’t know if I’m typical, but if I’m riding at night and overtake another cyclist without lights who’s not too much slower than me, I’ll slow down to give them the benefit of my lights. I’ve even done this with a (impressively fast and competent) rollerblader caught by the late-fall early sunset on the local multi-use path.

The interesting (to me) thing about these is that they can work in the US, they take no time to work, and they take no change in driver empathy or enlightenment. And if a crowd of bikes disassembles, then the safety effects do as well. The effects should appear most often at rush hours, when the largest number of bikes are on the road and when they are most hemmed in by traffic.

A historical/hysterical note is where the idea for safety-in-numbers comes from, and why we assume its existence even when we’re not entirely sure how it works. Once upon a time, when Effective Cyclists were peddling their prescriptions for safer cycling (ride in the road, in traffic, just like the “vehicle” that bicycles legally are, and that legal status is a good thing for which the EC movement certainly deserves some credit) the counterexamples of “the Dutch” and “the Danes” came up, where many people often ride bikes on lanes entirely separate from auto traffic, with crash fatality rates 5 times lower than ours. The EC people were very good at finding and/or interpreting studies that “proved” that if only the Dutch would get rid of their separate facilities, they would be even safer than they are now, that in fact their extraordinary safety must have some other cause. (This might even be true, but nobody’s ever managed to get more than about 1% of the population to bike in an “Effective” style.)

And what was the obvious difference that might be the cause of that anomalous safety? “Numbers”. It must be “Safety in Numbers”, assumed to exist to fill a (huge) gap between theory and reality. This was convenient for the Effective Cyclists because they got to continue to feel correct about their prescriptions (“just you wait, once everyone here rides bikes, we’ll be the safest cyclists on the planet!”) but now this same hypothesized mechanism is used to justify creation of cycling-specific infrastructure that Effective Cyclists hate (“we’re tired of waiting, EC is phenomenally unpopular and we’ll never get the numbers that give us the safety we want if we do it your way. And by-the-way, global warming, particulate pollution, pedestrian deaths, urban congestion delays, traffic noise, and public health, we need this now. Infrastructure will get butts in saddles and safety-in-numbers ‘proves’ that they’ll be safe.”)

I had tried to find this information myself in the past, but was unable to track it down. I had feared that something like this might be the case, but the actual numbers are far worse than I expected.

This is what years of gross inequality, overpaying for health care, overpaying for college, and the repeal of usury laws gets you:

For the median USAmerican, we’re not #1, we’re #17.

Mike the Mad Biologist lead me to this information.

If pitchforks seem too radical, try always voting for the viable candidate whose views are closest to Bernie Sanders. This usually means voting for a member of the Democratic Party, unless you are lucky enough to be able to vote for Senator Sanders himself.

An investment proposal

March 13, 2012

First, credit where credit is due. I read Mike the Mad Biologist. His post pointed me here, which mentioned an atrociously written Washington Post article (bad arithmetic, erased without comment, then corrected, with no reflection of the vastly different results in the text). This got me to think about buying efficient light bulbs as an investment, and so I did some interest calculations, as if the bulb were paying a mortgage.

I’ve long been interested in LED lighting, and have installed some myself in places where it was a clear win (underneath cabinets and on bicycles). I’ve been wary of “LED light bulbs” for some time, because to be fair, diplomatic, and objective, up till now, most of them have been overpriced crap. But last weekend or so, I was at the Home Despot, saw some LED light bulbs, read the labels, decided that it was worth my while to try one of them. I got a 14 watt bulb claiming to be the equivalent of a 75W bulb, installed it, and so far, so good — it’s bright, good color temperature, and instant-on, as expected. Lifetime is TBD; claims to have a 5 year warranty (but did I save the receipt? Whoops, need to remember to do that when I buy more), also claims to have a 25000 hour life, which is reasonable for LEDs. Also claims to be dimmable, but the reviews consistently say “no, not really, not like you’d expect”.

So, if I view this bulb as an investment, what is the rate of return? Let’s benchmark it against an incandescent bulb, since that is what the Post did. I initially decided to assume that I was saving 60 watts per bulb (15 instead of 75), running it 6 hours a day, and paying $.12/kwh for electricity (actually, I pay $.15, I just checked last month’s bill). Electricity savings come to about $1.30 per month.

Assume, also, that an incandescent bulb costs a dollar, and has a lifetime of 1500, so include the cost of the bulb in each month’s savings. At 6 hours per day, the bulb savings are 12 cents per month. Total savings are $1.42/month.

Assume the bulb will last 10 years (21600 hours at 6/day). I paid $30 for the bulb, plus sales tax, rounded up, is $32.

So, supposing I made an investment of $32, and it paid me back $1.42 per month for 120 months, at which point, no more payments, just as if I were loaning money to someone else for an itty-bitty mortgage. Spreadsheets have a “RATE” function that will determine the interest rate given a present value, future value, payment amount, and number of payments; in this case, -32, 0, 1.42, and 120. And out pops 4.4 percent. Not very exciting, though it helps that it is free of taxes, since it is money saved, not money earned. And if you only ran a bulb 3 hours a day, and only saved 45 watts, and only paid $.10 per killowatt hour, only 1.2%. That’s not much of an investment, is it?

But those interest rates are PER MONTH, not per year. So really, 1.2% — that’s 14.4% return, per year, tax free. If you return to the original assumptions, the $32 investment in an LED light bulb pays out at 52.8% per year.

What’s the risk in this investment? I see three possible risks that could cause it to fail to pay out.

First, you can only save money that you have; if you go bankrupt, then it’s not interesting that you aren’t paying money to the electric company, because you’re already not paying money to the electric company. However, all investments are vulnerable to bankruptcy risk.

Second, electricity in the next few years could become incredibly cheap (pigs could fly, too).

Third, the bulb could fail. Obviously, it pays to save your receipt; that gives you insurance of some sort for up to 5 years. If the bulb fails in five years instead of lasting ten, then the payout is not as impressive. If electricity is too cheap, or if you don’t run the bulb enough hours per day, it won’t pay out (3 hours per day, $.10/kwh, 45 watt savings, 5 years, will not pay off). But, if a bulb is on even 4 hours a day at $.10/kWH, the interest rate is 7.4%, or 3 hours at $.12/kWH, is 5%. Where I live with $.15/kWH electricity, 3 hours a day, 45 watts less, failing at 5 years, pays off at 14.8%. At 6 hours a day, 45.8%. I really like the idea of an investment that pays me 14.8% annual interest, tax-free, when it “fails”.

Did you notice that the Washington Post thought it was more important to tell you about the terrible government-subsidized light bulbs, when they could have been giving you this useful information instead? Says something about their priorities, doesn’t it? Hard to believe that anyone would think time spent reading that would be well-spent.

Headlight mounts always end up looking a little clunky, and are a little hard to adjust. This one works better than most I’ve tried, and looks better too (at least, relative to the others). You’ll have to take it on faith that the shape is pretty good, but the shape is pretty good, meaning, it throws a lot of light down the road, not too much too high, and makes a nice puddle around the front of the bike. I solve the light-in-eyes problem with low-beams; this one’s not too bad, but the amber low beams, mounted low, aimed low, are vastly better.

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There’s an internet cycling claim, attributed to Mayer Hillman, that not riding a bike (at all) is ten times more dangerous than riding a bike, because it is so unhealthy to be unfit. I haven’t been able to find the statistics that back up this claim, even when I bought the book from which it allegedly came Cycling: Towards Health and Safety. The closest it comes is the statistic that in a group of commuting cyclists, roadway crashes (of all kinds) accounted for only 1.4% of deaths (whereas heart attacks in this group killed 33%, and the known reduction in heart attack risk with exercise suggests a substantial net reduction in mortality).

However, happily, I just found this:

Even after adjustment for other risk factors, including leisure time physical activity, those who did not cycle to work experienced a 39% higher mortality rate than those who did.

Unless you think a 39% boost in your risk of death is “safe”, a little old unarmored bicycle, no belts, no airbags, no roll cage, is safer than a car, at least for the first 50-100 miles of travel each week.

And there’s more (via UtilityCycling.org):
Conclusions: On average, the estimated health benefits of cycling were substantially larger than the risks relative to car driving for individuals shifting their mode of transport.

About my (cargo) bike

June 19, 2010

I started riding much more seriously back in 2006, unhappy with my crappy blood chemistry, feeling fat, not particularly fond of the oil war that we were in, and global warming. I knew I could ride my commute — 10 miles — in good weather, not carrying much, but what about bad weather? What about shopping? What about kids?

What clinched the deal, was a few months after starting to ride in earnest, my blood chemistry improved, lots. Can’t quit now, right? So I didn’t, and set out to do whatever it took to keep riding. The bike I ride now is the result of this, and it is now a really excellent bike, probably more fun to ride than any other bike I have ever owned.

So why is it fun? It goes fast enough, it handles well, I can carry pretty much anything I can pick up, and because of the tires, steel frame, and the seat located midway between the tires, bumps are not so much of a problem. I can go into a sort of a tuck for the wind, I can ride upright and see everything, I can easily do a rolling dismount. It’s really stable; I come much closer to being able to do a track stand, and the bike tends to stay upright when I clip minor obstacles (don’t ask). If I don’t ride, I start to hurt; my knees like regular use, and there’s something funky (arthritis, is the unofficial diagnosis) going on in my back, that biking fixes.

Like all bicycles, parking is never a problem, like all bicycles, traffic is not much of a problem. Like all bicycles, if I find my way blocked by a giant snow pile or some similar obstacle, I get off and go around or over (try that in a car sometime). If it breaks, usually you can fix it on the road with hand tools. If it breaks badly (it did once) you can easily walk it home, or at least to a better place to wait.


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Fly, baby hawk, fly!

May 31, 2010

There’s red-tailed hawks nesting and fledging at 185 Alewife (across from the Fresh Pond mall, a busy place). This guy managed to fly into the building and land (fall?) in the parking lot. Everyone was getting worried that he had broken something, when he proved that he was ok.



(.5 second later) Go! (That’s a 1/800th second exposure, think he’s working those wings hard enough?)

Young red-tailed hawk, just taking off from top of car

He landed here:

Young red-tailed hawk perched on edge of building, with industrial backdrop

That’s him (?), right in the middle. Great neighborhood.

A standard response, when people compare cycling ride shares between the US and Northern Europe, is that “we’re spread out, they’re not”.

Except, of course, that we’re not.

Update/correction: the census data lists both New York City AND its boroughs, which is a substantial glitch. I found this looking at Wikipedia’s list of cities by density (also uses 2000 Census data), and cross-checking made it clear that there was a big error. The graph, as yet uncorrected, needs to be shifted down by 6 million (minus 8 million for NYC, plus 2 million counting the contribution of the smaller, very-dense places). I would like to incorporate the smaller dense places more generally, but don’t know where that data is yet. Most of the conclusions remain the same; the 10% mark is now at 7600/square mile, and the 1/3 mark is now at 2000/square mile. Read the rest of this entry »

brought to my attention by my wife, who got it from someone else.

The Simple Sabotage Field Manual, declassified, on interference with organizations and production.

Description: http://cgsc.cdmhost.com/cdm4/item_viewer.php?CISOROOT=/p4013coll9&CISOPTR=307&CISOBOX=1&REC=11

PDF: http://cgsc.cdmhost.com/cgi-bin/showfile.exe?CISOROOT=/p4013coll9&CISOPTR=307&filename=308.pdf#search=%221944%22
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Snow Tire Review

December 12, 2009

I’ve tried Nokian Hakkapeliitta W106, Schwalbe Marathon Winter, and Schwalbe Snow Stud.

And more recently, Nokian W240.
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