On June 22 Cambridge held a public meeting on traffic in Inman Square. I did not attend. I did receive a pointer to the presentation. The next day, a woman on a bicycle was killed in Inman Square, perhaps first doored, certainly run over by a landscaper’s truck.

Preliminary comments.

Slide 4, I see counts of “traffic volumes” measured in “vehicles per day”.
Which of the following is “vehicles”:

  • bicycles only?
  • cars and trucks only?
  • bicycles and cars and trucks?

I see no pedestrian counts, which seems like a major omission.
I also see no breakdown by turns, which makes it difficult to know how much of a priority to place on turning traffic.
I also don’t see any information about existing light timings.

For slide 13, the only group for whom “increase efficiency” is a concern is “Vehicle”, and I suspect that really means “Motor vehicle” since “Bicycle” is a separate category. This seems like a major omission, since you have apparently not measured either the bicycle traffic or the pedestrian traffic, we don’t know if optimizing motor vehicle efficiency reduces the total time wasted at this intersection, and it might well compromise safety. Lacking any other information, I think we must assume that each person traversing this intersection is equally important.

It’s also important to notice that attempts to “increase efficiency” for motor vehicles here could be pointless. This intersection doesn’t exist in isolation; it is connected to the rest of Cambridge, which is also filled with traffic jams. In contrast, both bicycles and pedestrians flow freely through the rest of Cambridge (I bicycle commute on Broadway or Hampshire every working day of the year, I have video) so impediments removed here would result in actual gains.

One efficiency problem that could be addressed with no infrastructural changes is locally-greedy misbehavior by drivers; people frequently enter the intersection without a clear path to exit it, resulting in a blocked box when the light changes (bicycles are less affected by this; again, I have video). Drivers also speed fruitlessly (later to be passed in a line of stopped traffic by a fat old man on a huge heavy bicycle, so truly useless speeding), endangering everyone. In both cases, the remedy for locally-greedy misbehavior is enforcement; tickets for blocking the box, tickets for speeding, tickets for running red lights. Automated enforcement is probably more cost-effective than staffing the intersection every day at rush hour.

Another thing I saw no mention of was the role of parking in reducing safety. The door zone is a constant worry to cyclists, and the space allocated to parked cars also reduces options for creating safe places for cyclists to ride.

Other questions that need answering:

  • I know that buses use Hampshire. How many people use those buses, and how much delay (summed over all the bus passengers) results from that delay? That’s another thing we should optimize.
  • There’s a lot of bike traffic on Hampshire, especially at rush hour. If we knew the range of trip distances for people traversing Inman Square in cars (especially at rush hour), we might get some idea of the potential number of bicycle commuters that would use Inman Square if were less dangerous and more pleasant (it is one of the more significant unpleasantness bottlenecks in Cambridge).

Given what looks like a severe case of car-centric tunnel vision by whoever prepared these slides, I think that someone needs to start over again, perhaps doing the mental exercise of banning cars and seeing what sort of intersection results. (That’s not quite a serious proposal for an intersection design, but it is definitely a serious proposal for being sure that something other than cars-cars-cars is considered.)

My choice for a starting point would be to de-emphasize traffic “efficiency” for single-occupancy vehicles since those are the least-efficient users of scarce road space, the most needy in terms of a clear path to travel, and relatively dangerous to other people on the roads. Buses are space-efficient, very safe for their passengers, necessary for the less-able, and a good backup choice in nasty weather. They’re not a good thing to crash into, but their drivers are trained professionals, and risk-to-others is amortized over all the passengers on the bus and thus is not that large per passenger. We should remove enough cars from the road to ensure that buses are not impeded. Both bicycles and pedestrians are very space-efficient and though neither mode is risk-free, they are very safe for other people, and they’re also able to cope with narrow paths and impediments that completely block automobiles. I would therefore do as much as possible to make those two modes attractive. When I look at all the somewhat-unused space in Inman Square, my reaction is to try to find ways to use that space make things better for pedestrians and cyclists, instead of trying to use it as more places for cars to drive on.

Videos of Inman Square:

Subway capacities

May 7, 2016

I recall once figuring that the capacity of a single track of subway was substantially higher than a lane of traffic. This is how that is calculated for a real live subway (the MBTA Red Line, also roughly applies to Orange and Blue lines which run similar equipment.)

redline_cars_per_train = 6

Source: Wikipedia red line article

redline_trains_per_hour = 60/4.5 = 13.3

Source: 2014 MBTA Blue Book, page 17.
Headway is 8 or 9 minutes at rush hour on each of the Alewife/Ashmont and Alewife/Braintree lines, or 4.5 minutes on average on the shared portion of the line.

redline_ppl_per_car_policy = 167
redline_ppl_per_car_crush = (267*74+260*58+277*86)/(74+58+86)

Source: 2014 MBTA Blue Book, page 18.
167 is the policy people-per-car. Seated and crush capacities are averages over the red line fleet.

seated_rush_cap = redline_ppl_per_car_seated * redline_cars_per_train
policy_rush_cap = redline_ppl_per_car_policy * redline_cars_per_train
crush_rush_cap = redline_ppl_per_car_crush * redline_cars_per_train

seated_rush_cap * redline_trains_per_hour => 4,671.5596
policy_rush_cap * redline_trains_per_hour => 13,360
crush_rush_cap * redline_trains_per_hour => 21,526.6055

Compare this with a lane of traffic. Rule of thumb is that you get one car every two seconds, or 1800 cars per hour, and an average of 1.2 people per automobile, or 2160 people per lane per hour. Simple seated subway capacity at rush hour is double that, so-called “policy” capacity is 6 times that. Crush capacity, which I’ve seen and not much liked (“nobody takes the subway, it’s too crowded”) is just shy of 10 times the capacity of a lane of traffic.

And understand, this is far from the theoretical capacity of a subway line, it’s just what is actually obtained on a real subway in a real city at rush hour. Run longer trains (requires longer platforms, a completely doable thing) and you can add capacity. Run trains more frequently, and you raise capacity – the London Underground appears to manage 24 trains per hour at rush hour on the Northern Line or not quite double the Red Line’s frequency.

Re-doing the numbers at the London Underground’s rate for scheduling trains:

seated_rush_cap * underground_trains_per_hour => 8,408.8073
policy_rush_cap * underground_trains_per_hour => 24,048
crush_rush_cap * underground_trains_per_hour => 38,747.8899

At the Underground rate, “policy” train packing carries 11% more people than “crush” packing in the current system. And the theoretical “crush” capacity is the equivalent of 18 lanes of traffic.

Earlier this week, I was riding my bike home on a road with a bike lane, and came up to an intersection where the car at the front looked like it was planning to turn right (based on position in lane and angle of wheels) but was not signaling a right turn. The intersection has no advanced stop line for bicycles, just a plain old stop line and crosswalk. And understand, me going first is a completely legal thing, there are two lanes, straight traffic has right-of-way over turning traffic.

This presented several choices. I could stop far enough back that if the driver intended to turn right, they could easily do so (except that they would probably get hung up by pedestrians in the crosswalk and would stop midway, blocking the bike lane and delaying me). If they did manage to turn right quickly, there’s no guarantee that the driver behind might not try to barge on through with their own right turn; that’s happened, I even have video of someone doing this. Or, I could pull up to the stop line, and hope that if they did decide to turn, that they’d notice my presence in time not to hit me, and also not try to just make their turn through intimidation. Or, (and this is what I did) I could stop a little bit in front of the stop line – technically illegal, though I’ve never, ever seen this particular law enforced and drivers violate it constantly – and position myself so that the driver could hardly help seeing me, and even if he didn’t or if he decided to go anyway and there was a collision, I’d land on the hood of the car – relatively safe for me as collisions go, relatively damaging to the hood of the (expensive) car.

I hope it’s clear that this is no way for a normal person to ride a bicycle. I do so because I’ve learned it over the years and it’s no longer difficult, but to think that I would explain this to someone else as “useful tips for riding in traffic” is insane. This is similar to knowing that “it’s okay to ride closer to parked cars in a residential permit parking zone, because people move those cars only about once a day”. Or, “practice riding through potholes no-hands, so you get really good at controlling your bike on our crappy crappy roads”. I’m not making any of this stuff up, I do these crazy things, our roads are messed-up enough that it helps.

I’m not sure how this gets fixed. Safety-in-numbers is some mitigation; with enough people on bicycles, it becomes obvious that there’s bike traffic to the right and bike traffic through intersections and bike traffic past car doors, and the normal distribution of aggression among bicyclists insures that a few of them will help carve out space for the rest. I don’t put much stock in driver education; there’s not that much in it for the drivers, and it’s work to constantly be looking around for bikes. We could pretend to do more enforcement, but in practice the majority has zero appetite for that (evidence: we don’t vote for more enforcement, despite continual infractions and drivers killing thousands of themselves and other people every year). I think I’d like it if we adopted some modern Dutch infrastructure; a lot of that is designed to get rid of these designed-in conflicts and make it easier to see what’s going on. I have some hope that robot cars might be helpful; tedious rules like “always signal a turn at least 10 seconds or 3 car lengths before the turn” are what computers are for, as is “look for bikes in all directions always”.

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…”).