I both drive cars and ride bikes, and for years I didn’t think much about how much driving a car impairs all your senses, as well as your ability to communicate. To hear how other people talk about traffic and safety, I think I’m not the only person to miss this.

Where this usually comes up is in discussions of rolling stops, and stop-then-go at red lights. The claim from cyclists (and this claim is absolutely true, which is why I’m writing this) is that they generally can see and hear better than people in cars, and thus are in a better position to judge if it is safe to go or not. This is one of the several justifications for the Idaho Stop Law.

So, vision. Someone riding a bike is as tall as they are standing up, if not taller. To stop, most people must hop off the saddle because they sit too high to reach the ground with their feet. Modern sedans tend to be about 4-and-a-half-feet tall (I just measured a Civic and a Camry), so whoever is sitting in them is shorter than that. On a bicycle, seated, your head is about 3 feet back from the front edge of the bicycle, but it’s easy to lean forward to within about a foot of the front. In a car, leaning forward gets you to the windshield, which is five feet back from the front of the car. Add to that whatever fog or dirt happens to be on the windshield and the windows, plus the various pillars and mirrors and fuzzy dice, and I hope it’s clear that the cyclist has a far better view of what’s around.

Next, hearing. Luxury cars are actually marketed for their ability to make you deaf to the world. That ought to be enough right there, but I’ve actually mentioned this to a degreed+prestigious colleague whose snap reaction was “no, I can hear okay in a car”. No, really, you can’t. Even without luxury soundproofing, cars have noisy engines, ventilation fans, tire noise, often a stereo, and quite often their windows are up. All these things act to block exterior sound. On a bicycle, the default is that you hear everything. There’s wind noise when you’re moving, but stopped at an intersection there’s nothing between you and the world and the bike is silent.

And you might like to think that maybe hearing doesn’t matter–after all, we let people who are deaf drive and ride bikes–but it certainly does. When I approach intersections, I can hear cross traffic coming before I can see it; that’s redundant safety information, which is a good thing. I can hear cars approaching from behind, and tell if they’re slowing or swinging out into traffic to pass, and I can judge the size of the car or truck as well (big trucks without sideguards are very dangerous). For pedestrian safety being able to hear matters, because I can carry on a conversation with the people around me. “I see you”, “go ahead, it’s a crosswalk, I’m stopping”, and of course “oops, sorry”. I can communicate with other cyclists, “there’s a blind woman walking ahead of you” (in the dark). All the sound signals that we’re supposed to legally make when approaching pedestrians are useless when approaching cars because drivers are effectively deaf. All the communication that’s easy with people around us is impossible with people in cars.

People on bikes also see more because of their ability to always position themselves near an intersection before stopping. That means we always get to see the light cycles and light timings, and even if we haven’t learned them all yet ourselves, we can see how other cyclists react to them. We don’t need to catch sight of landmarks as we drive through the intersection, because we always have plenty of time to look around at the front. Once you know the usual timing for a light (easily derived from countdown pedestrian timers on the street and cross street – which you can see because you are stopped at the intersection) you can also judge from quite a distance the appropriate speed to make the next light, which allows you to moderate your speed to only what is adequate to catch the green. Lower speeds make for easier pedalling, and are also safer.

I had meant to make a much longer rant about “windshield vision”, but I think this is good enough for a start. You might ask yourself, if you could drive and fool yourself into thinking that you weren’t half-blind and mostly-deaf, and not realize what you were missing stuck back in a line of traffic, if you might not be self-fooled about some other things. If your reaction to the facts stated here is that they’re the crazy opinions of one of “those cyclists” – don’t forget, I am a licensed driver, I drive often enough, I own a car, and this is true of most adults riding bicycles (knowing this stuff makes driving a lot less fun. Don’t expect any auto advertising to mention this ever).

Bonus sensory deprivation video, in case you still don’t believe me: watch the second driver in this video roll right over a bicycle and a bicyclist’s foot, and not be able to believe she did it. Said bicyclist has right of way, in clear daylight, riding straight on a straight road, wearing a dayglo-yellow jacket, with a front flashing light. The second driver did not see, did not hear the crash, did not hear the crunch of the bike as she drove over it, did not hear the guy she was running over yelling at her.

It occurred to me a few days after posting this that “people on bikes behave unpredictably” is consistent with “people on bikes make decisions based on information I don’t have”. Probably not the only explanation, but worth thinking about before jumping to pejorative conclusions.

I did a round of noodling in a spreadsheet to try to get a feel for how different ways of carrying people or cargo damage roads. The formula for damage is the sum of the cubes of the wheel loads; crudely, the gross weight of a vehicle cubed, divided by the square of the number of wheels. This can lead to some pretty non-intuitive results — city buses in particular are non-intuitively bad for roads .  Overall the most surprising thing is that even when results are calculated either per-passenger or per-pound, you end up needing a log scale to display them meaningfully; heavy vehicles are that bad for roads.

I’m not quite sure what to do with this information; there are other things to optimize for besides road damage.  For example, it would not surprise me in the least if a semi-trailer were more fuel-efficient per-pound than a human on a bike; bikes are efficient, but we do have to eat to run them and food is quite often energetically costly.  Similarly, though bicycles are far safer for pedestrians than cars and trucks, per pound of cargo they will lose most of their advantage against delivery vehicles (the comparison is quite tricky; a cargo bike can easily carry 100 lbs in addition to its rider, and 250 is not out of the question, and such large bicycles are even less likely than “normal” bicycles to travel at pedestrian endangering speeds.  Contra that, a human pedaling a loaded cargo bike has an incentive to not stop because it takes quite a lot more energy to bring that larger weight back up to speed).

Note that a single-occupancy vehicle still fails badly on efficiency and safety metrics, but trucks of various sizes need not.


This is a half-baked theory based on no particular expertise of mine, but I’ve been reading and thinking about safety for a while now (perhaps decades).  I have come to think that one contributor to driver irritation with cyclists is that drivers are already driving about as fast as they can think (if not faster) and the sudden appearance of something out of the ordinary like a cyclist in traffic is the straw that breaks the cognitive camel’s back; the driver is no longer able to keep track of everything that is going on and they don’t like it.

Several things led me to this.  One was things like the awareness test video, where it is made obvious how our attention can become so focused by cognitive load that we will overlook what is right in front of us. Another is my use of daytime running lights; I started doing this years ago because when I built my own lights I left out the off switch (it’s just another point of failure).  With lights on all the time I am more visible and less likely to surprise, and it seemed that I had many fewer unpleasant interactions with drivers.  They were still often-enough clueless and no more likely to obey traffic laws, but they seemed to almost never be angry with me.

A third thing is the experience of riding the bike itself.  My bike is relatively tall (has a high bottom bracket) and I am slightly tall (6′) I am riding upright, and rarely going even 20mph.  I can see around me much better than when I am driving, and because I am almost always moving at a reasonable pace I have plenty of time to consider what I see.  And once you get used to this, the lack of it is unpleasant — when I’m driving, I notice that I’m deaf, and I don’t like it (I roll down the windows, whatever the weather — what’s more important, safety, or not getting a little rain blown in the window?), and I notice that I’m short and can’t see as much, and I don’t like it, and I notice that stuff is happening too quickly to pay proper attention to it.  I think most only-drivers are accustomed to a different baseline than I am, but when they fall off that baseline they don’t like it, same as I do, and blame the distraction for their irritation.  In my case, I blame the car that I am driving, in their case, they blame the cyclist, pedestrian, or whatever it is that happened to cause their cognitive overload.

Another application of this is in devising safety rules.  One rule that serves me well on my bike is to count the number of potentially unpredictable things (dogs, small children).  One is usually not a problem because I can swing wide of it.  Two, I should slow down some, depending on details.  But three is more than I can reliably track; I should slow down to a walk, if I cannot put a safe distance between me and the children/dogs.

Or, when approaching a crosswalk with pedestrians in it, how do they know that I intend to stop?  Sure, I could slow down, but that means that they have to track me long enough to know that I am slowing down, and what if I wait till the last minute — that all combines to add an unnecessary cognitive task for those pedestrians.  That’s rude.  So I slow early so it is easier to see that I know I should stop, and I signal so that they don’t have to track, and I aim the bike behind their path so they can see that I think they should be crossing.

Field trip to NYC

October 1, 2015

So I’m attending a conference in NY on Friday, took the train down Thursday and spent the afternoon at the NY office, took Citibike to get there from Penn Station and then back again to the hotel.  Most of my riding was on 8th and 9th Avenues, which have nice segregated bike lanes.  I observed the following:

– sidewalks in NY are too small.  Pedestrians regularly spilled over onto the bike lanes, and it’s because the sidewalks are crowded.  Obviously the sidewalks need to be larger, because we cannot make pedestrians smaller, and they are the overwhelming majority here.

– no matter what anyone says, bicycles are not terrifying relative to cars.  I didn’t see any pedestrians walking in the flow of traffic because the sidewalks were too small.

– salmoning is about 100x more common here than in Cambridge (MA).  I see it there in-my-face about once a month, here, I’d say at least a dozen times in less than an hour of riding.

– in the places where the bike lanes were not segregated (by a line of parked cars) everything dissolved into nonsense.  Cabs drove in the bike lane, bikes rode in the cab lane.  The should rip it out and do it again.

– but where the lanes were segregated, it worked really well.  It was quite comfortable, I did have to take care to not hit people on foot, but that’s not hard (I’m on a Citibike, not exactly racing along).

– cars driven in NY should have their horns removed.  I know the horn law in this state, horns are only for safety, “the light is green but you’re not moving” is not a safety issue. Period. (Go ahead, try to argue the case that it is, make a fool of yourself.  Stopped cars are the safest cars.)

I saw the arguing aftermath of a pedicab-bike collision — didn’t understand why on earth the guy on the bike was pressing the point because I saw nothing hurt and nothing broken, but he was.  I blocked more than one NY taxi from making a right turn when it came into conflict with the bike lane.  I saw one person on a bike who was trying to make a big deal about clearing pedestrians from the bike lane (“ha ha, she has got to be kidding…”).

1000 miles to the new job.

October 1, 2015

(written in July, now it’s October) I got a new job 4 months ago, now in Kendall Square all the time.  I only bike to work, unless I work from home (done that 2 or 3 times so far) and I even commute by bike when I visit the mother ship in Mountain View.  In 4 months I accumulated just about 1000 miles to work, a combo of neighborhood streets, bike lanes, cycle track, sharrows, and fitting in wherever it is appropriate.  October update — 1750 miles now, about 250/month, and writing this from NYC where I rode Citibikes to/from the NY office today.

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I’ve noticed that car drivers on the internet often think they are qualified to lecture “cyclists” on how to be safe. This is ludicrous, given that the average driver is 10 to 20 times as likely to kill a pedestrian as the average cyclist, with a similar ratio for serious injury, and the cyclists are mostly car-owning licensed drivers anyway. “But cyclists break traffic laws”. Number one, they only do so about as often as drivers – people are people, we all make mistakes and take shortcuts, and we all also overlook the faults of our own tribe and are hypersensitive to those of “the other” – and number two, if you really think that cyclists DO break laws at some unusually high rate, then that means that laws have not much at all to do with true road safety. Recall that bikes are 10 to 20 times less likely to kill or seriously injure pedestrians than cars – that’s safety.

So, if cyclists don’t obey laws, what do they do that makes them so much safer? And wouldn’t it be great if drivers knew about this, so they could do these things too, and be much more socially responsible? I’m sure they’d really like to know, so I will BikeSplain safety for them:

  • around bikes and peds, 20mph is plenty. Not 21. 20. And in general, never build up speed you don’t need; if the light is red, why not coast as soon as you see the red, instead of going fast and then braking at the last moment. Speeding-then-braking is a waste of energy and poses unnecessary risk to others.
  • do not use a larger vehicle than necessary for the errand. 100lbs (a large cargo bike) is adequate for 3 kids, groceries, etc, if you’re only traveling a few miles. This holds true even when choosing one car over another, if you have a long or hilly errand, or if you are handicapped in some way; an SUV is over 3 times more likely to kill someone else than a regular-sized car.
  • windows down, stereo off. You need to be able to hear what’s going on around you. With the window up and stereo on you’re effectively deaf, and you’re certainly less able to hear than a cyclist using earbuds (yes, someone has tested this).
  • if you’ve been drinking, it’s good to always pass a small challenge of coordination before embarking on a journey to be sure that you’re sober enough to drive a car. For example, if you cannot keep a bicycle upright for more than a block or two, you are surely too drunk to drive. So if you’ve been drinking, even a little, be sure to ride a bike first as a test to see if you’re sober enough to drive.

Almost every cyclist on the road obeys the rules above, and that’s the main reason why they’re so much safer than drivers. The one exception is people who are training to race – they often travel faster than 20mph and are less safe for pedestrians, but fortunately they are a small minority of urban cyclists.

Many cyclists follow additional safety rules to obtain even more safety. I use these rules myself, and I’ve seen other people do the same:

  • never use your horn or bell. Use your brakes instead. Think about all the stuff that has to go right for your horn to make things safer, versus the certainty that you see something going wrong and could start slowing down right away to either prevent it or mitigate it. With the windows down and stereo off, you might be able to even talk to the people around you.
  • if you can imagine a potential crash, act to reduce its risk and/or mitigate it if it occurs. No free pass just because you think the other guy is breaking a law. How sure are you about traffic laws? And so what if they are breaking the law, is dead an appropriate outcome? Is that guy with the leaf blower going to stumble backwards into the road? If you see a teenaged boy on a bicycle or driving a car, what are the odds he might do something irresponsible? Drive as if that might happen, and be prepared to keep it from causing a crash.
  • reduce speed limit by 5mph for each child/dog (up to 3) near your path, i.e., 15, 10, 5. It’s unlikely that you can keep track of 3 unpredictable moving objects at once, and even trying will distract you from everything else you should be watching. So slow down, to give yourself more time and to mitigate the harm of any crash that might occur.

In the spirit of “Same Roads, Same Rules”, I think these are good rules for everyone to follow, both in cars and on bikes.

Cost of a lane of parking

September 6, 2015

The Green Line Extension in Somerville and Medford is part of the (legally mandated) environmental mitigation for the Big Dig freeway-burying project. Like other parts of the Big Dig, there have been cost overruns and bloats in estimated cost, and it is now projected to cost $3 Billion for 4.3 miles of trolley rail.

Another way to spend money would be to remove parked cars from roads and use the extra space to establish dedicated lanes for buses (and perhaps bicycles, not sure how well that works in practice). But what would that cost?

Generously, I estimate 500 cars per mile of road – 10560 feet of road (both sides) divided by 20 feet per space, minus a dab for hydrants, driveways, cross streets, and 500 is a nice round number. The Metropolitan Area Planning Council estimates $20,000 or more to construct an urban underground parking space, not counting land. That gives a construction cost of $10,000,000. For land, compare with the Alewife parking garage, which uses 5 acres for 2733 cars, none parked underground or on the first floor. This suggests an acre, and hopefully the ground floor can have some more productive use than car storage. In Somerville, extrapolating from some recent home sales on Zillow, an acre of land costs $11 million. Call it $15M for the sake of conservatively round numbers.

Thus, the round-numbers replacement cost of a mile of both-sides street parking is $25million, or about $50,000 per space, plus annual maintenance (according to the MAPC) of up to $2000 per year. There are plenty of related costs and benefits – if there’s only one garage per mile, some people will have long-ish walks, but on the other hand the parking will be mostly covered and thus not require shoveling out in the winter. It’s likely that parking would be distributed into smaller hunks to simplify land acquisition for garages and to reduce the walking distance.

$50,000 for a parking space may sound like a lot of money, but compare it to the cost of an 8’ x 20’ piece of land at $15 million per acre. Do the math, and you get about $55,100 per parking space.

Doing this benefits us in several ways. Because buses can move more quickly, they provide a more valuable service to their users. Because buses can cover the same distance in a given amount of time, either service can be more frequent for the same cost, or else fewer buses are needed to provide the same service intervals. Street plowing and cleaning become easier, and emergency vehicles can flow more freely during rush hour. Crossing streets becomes slightly safer because parked cars will no longer obstruct views between pedestrians and drivers; each can more easily see the other. Removing parking also eliminates the cause of bicycle dooring (20% of the crashes recorded in Cambridge) and both improved visibility and the availability of the bus lane as a refuge from traffic are likely to improve bicycle safety.

There is an economic side-effect of making the cost of parking more salient; if the city is paying off a bond on a parking structure or has a budget item for parking structure maintenance, that will encourage a critical comparison of the cost of parking versus the cost of alternatives. Right now the default treatment of parking is as if it is “free”, as if there were not even any tradeoffs to be made. This doesn’t sound like a good thing to someone who is currently benefitting from free or subsidized street parking, but from an economic point of view it is likely to lead to a more efficient allocation of resources if we recognize their costs.

To return to the Green Line, its original $2Billion cost estimate would be adequate to remove parking from 80 miles of streets.

This comparison needs further work. “86% drive to work” is 86% of the working population, not the entire adult population, though to the extent that this reflects non-employed behavior it’s not complete crap.

But also note that I used the most conservative estimate of bicycling’s health benefits.

It turns out driving to work is indeed a public health issue. I did the math a hair more carefully, and over the entire population it looks like driving to work causes about twice as much 20% more early deaths than cigarette smoking (note that this is a difference of a difference; the overall annual mortality rate with smokers is 18% higher than not; the overall annual mortality rate with drivers is 21.5% higher than not). From OECD, Cycling, Health and Safety, pdf page 44, table 1.2:

“Relative risk expressed as a ratio of all cause mortality of cyclists compared to non-cyclists after controlling for confounding factors (age, gender, education, etc.) – e.g. a relative risk result of 0.70 indicates that a cyclist has a 30% reduction in risk of death compared to a similar non-cyclist.”

Location Relative mortality risk (cycling/non-cycling) Confidence interval Study
Copenhagen 0.72 0.57–0.91 Anderson et al, 2000
China 0.79 0.61–1.01 Matthews et al, 2007
China (HA) 0.66 0.40–1.07 Matthews et al, 2007
Finland 0.78 0.65–0.92 Hu et al, 2004
Finland (HA) 0.69 0.57–0.84 Hu et al, 2004

(HA) = “high activity”

A “relative mortality risk” of 0.79 (call it 0.8 for ease of math) means that in a given year a cyclist has only 80% of the risk of dying of a non-cyclist – or if you view the choice to not ride a bike as the abnormal behavior, a non-cyclist has a 25% (0.2 added to 0.8, 25% of 0.8) higher risk of death.

This is not as bad as smoking per-person – that about doubles (adds 100%) to your mortality risk – but only about 18% of the population smokes, and 86% of the population drives to work. Weighted by exposure, driving to work is a larger public health problem than smoking. (If 18% of population quit smoking, 18% of population cuts their 2x normal death rate in half, a 9% drop. If 86% of population quits driving to work and starts walking or biking, 86% of population cuts their death rate by 21%, an 18% drop.) (Math error: based on these numbers driving to work is the larger problem, but it is a 21.5% increase against an 18% increase.  From Calca:

.18 * 2 + (1-.18) * 1 => 1.18
.86 * 1.25 + (1-.86) * 1 => 1.215

Note that this says nothing about whether we make it easy for people to stop smoking or stop driving so much. Absolutely it is hard, I have friends and relatives with commutes that are completely impossible on a bicycle, or walking, or transit. We have chosen to make it hard for people to live healthier lives, and we should stop doing that. We need more transit from far-flung suburbs. We need safer streets to bike on, both in suburbs and in cities. We need greater density closer to work. Because our towns can’t necessarily afford greater density because of the property tax expense of serving all those extra people, we need to change how we fund things like education. Broken policy should be fixed, not used as an excuse.

Smugness Accomplished!

August 15, 2015

I had once lamented that, though it is tiny, bicyclists do benefit from some small subsidy for their use of the roads, and that this undermined our goal of attaining peak smugness. Somehow it escaped my attention that gasoline is only taxed with a “gas tax” and not with a “sales tax” – yet bicycle chains, tubes, and tires (the three items that are consumed every few thousand miles of bicycle use) are taxed, with a sales tax. If the sales tax is 5%, even the heaviest cyclist (e.g., me, on a loaded cargo bike) need only spend about $20 per year on these consumables to be adequately taxed for their use of the road.

It ought to be obvious, but we’re done here. Bicycles not only pay the full cost of their wear and tear of the road, they pay more. Drivers only pay about half – the rest is subsidy from other taxes besides gas taxes, excise taxes, and tolls. Smugness accomplished!

At special town meeting last night we discussed a portion of the road and green redesign for our town center. A central question was whether we should push for yet more parking and maintain an existing shortcut for drivers. One person speaking in opposition tried to make the case for how ridiculous it was to expect people not to drive, because after all, he’s not as young as he used to be.

That is, being old, fat and out of shape is supposed to be a good reason to not ride a bicycle. This is bullshit. Being old, fat, and out of shape is one of the best reasons to ride a bicycle. It’s one of the main reasons I ride a bicycle so much now.

I didn’t speak at town meeting, though I do in fact know a proven solution to most of the problems that worried people, because most people are too damn scared of change. Lots of people talked about their problems with backed up traffic in town center; I never have that problem on my bicycle, I just filter through. Lots of people talked about the difficulty of finding parking; I never have that problem on my bicycle, I just lock it up any old where (“but what if everybody did that?” “If everybody rode bikes, we’d steal 5 parking spaces and convert them to space for 60 bicycles. We need more problems like that.”)

Again, if your only problem with biking is that you’re “too” old, fat, and out of shape, you are looking at it all backwards. And if there’s no good places to ride, complain to your selectmen, complain to your town meeting members; plenty of them are tremendously worried that driving – in 4-wheeled, armored, shock-absorbing, climate-controlled motorized comfy chairs – might be so inconvenient that people would just drive somewhere else to do their shopping. I don’t think it’s the least bit unreasonable to request that the roads at least feel safe to ride a bike on.