Outside of work, I really like to ride my bike. I’m not really interested in racing or the competitive side of cycling; but I love the experience of it, which always feels a little like flying, and I love how much you can see a city from a bike. It’s like a whole other way of seeing the world that you can’t get from walking or any other kind of transportation. I moved to Chicago when I was 23 and my bike was my main form of transportation for years. I never owned a car in those days; I just rode my bike everywhere. There was a year when I had a 13 mile daily bike commute — I don’t think I have ever been in such good shape. It’s world-changing, somehow, to spend so much time doing this activity.

Unfortunately, riding a bicycle in a city can also lead to crashes. It is objectively somewhat risky.

So every time I have any crash or incident, I’ve started to do a risk analysis afterwards, to see what I could do differently in the future. (Here, it starts to intersect with professional software development just a little bit, inasmuch as formal risk modeling is part of software engineering.)

Ideally, if you find out what scenarios are likely to cause bike accidents, you can avoid putting yourself in those situations again.

Over time, I’ve formed a list of rules for bike riding.

Basic rules

  1. Reduce speed. Speed is one of the biggest risk factors while biking, because it makes accidents more likely and it also makes them so much worse. Kinetic energy is proportional to the square of your velocity, so every time you double your velocity, a crash will have 4x as much energy to dissipate into your body. Also, speed reduces your reaction time; the faster you go, the less time you will have to react to any approaching risks. So, Rule 1: don’t go super fast. (I enforce this for myself on my road bikes, which have front and rear gears, by almost never shifting the front shifter into the biggest (outer) ring - I figure that the increased safety is worth going a little slower.)
  2. Scan the road surface carefully and continuously. Mentally note any bumps, dips, cracks, grooves, potholes, drains, grates, speed bumps, or any other imperfections in your path, so that you have a detailed picture of exactly what risks are approaching on the roadway. Over time, you can develop intuitions about how your bike will interact with any given obstacle (“this small bump will be fine,” “this sudden dip in the road looks dangerous,” or “this is a huge bump and it’s too late to avoid it, eep, hold on tight”).
  3. Constantly scan the environment for all other vehicles, bikes, pedestrians, or any other moving objects. Estimate when or if they might intersect your bike’s future trajectory, or, worse, if they might hit you based on their current path.
  4. Scan behind yourself for any approaching vehicles. Especially check when you hear noises, or if you are considering moving farther left into the travel lane.
  5. When possible, make eye contact with approaching people or vehicles, or wave at them. You want to communicate with people so you can establish mutual awareness and (ideally) respect. You want to be sure that they know you are there, and if possible, ensure that they are planning not to hit you. I usually try to make eye contact first. If I’m not sure that eye contact is working, I might wave at them too. People’s eyes tend to notice motion.
  6. Choose your trajectory carefully and precisely on the road. Choose your path to avoid obstacles and minimize risks, given everything you know about the situation around you, and given your state of communication with other people and vehicles. (The longer I ride my bike, the easier it is to place it precisely where I want it to go on the road.) You might want to ride closer or farther to the curb; you might want to avoid obstacles or go over them; you might want to slow down or speed up. The point is, you are making all these choices in view of the situation.
  7. There is a flip side to the last point: Don’t change your trajectory without knowing what’s happening around you, especially what’s behind you. Just because you see an obstacle in your path, this does not mean it is safe to swerve out of the way - you could be swerving into a new problem. (In emergencies, you might need to swerve without being absolutely sure of what’s behind you; this is a risky choice, even when it’s necessary.)
  8. If you spot a dangerous situation like a possible collision approaching, remember that you have more than one option for how to avoid it. Obviously, you can hit the brakes and slow down. But you can also steer out of the way or, unintuitively, you can also speed up. (Speeding up is a perfectly valid strategy for avoiding collisions.) Obviously in a real emergency you won’t have much time to think about your options, but it’s good to know in theory that you have more options than just hitting the brakes.
  9. It is OK to just pull over and stop momentarily if you need to. For instance, sometimes when an obstacle is approaching (a parked car in an otherwise empty street), instead of moving farther out into the road and going around it, I pull over and stop for a few seconds to let traffic pass me, and then continue.

Intersections and traffic

  1. Respect traffic signs and signals the same as a car, especially if there are any cars around whatsoever. It makes drivers mad at you if you openly ignore the traffic signals and stop signs. It is also just safer and easier for everyone if you respect the traffic rules. This is one way we can help to create a consistent, predictable environment.
  2. Intersections are generally high risk places. Always assume that car drivers don’t see you until they have proven otherwise. Assume people might ignore the traffic signals (for example, they might keep going after the stoplight turns red). Don’t enter an intersection until you are sure it is safe.
  3. It’s often safer at intersections to join the vehicle traffic and wait your turn than to try to dodge along the side of a line of stopped cars. You do have a legal right to do this as well, for what that’s worth.
  4. Driveways are also dangerous, though not as dangerous as intersections, because people entering or leaving a driveway don’t always see you. Check driveways as you pass for signs of motion. Slow down if you are approaching a driveway and can’t see what’s inside, like if it is behind a construction fence or a gate.
  5. Never ride on sidewalks unless you are accompanying kids on a bike ride.
  6. Bike lanes at the edge of the road are a missed blessing. Cars don’t always pay attention to them. People tend to park across them, meaning you will have to go back out into the vehicle lane. Bike lanes tend to have more debris, fallen leaves, and broken glass. Don’t avoid bike lanes, but use caution.
  7. Especially beware of bike lanes at intersections, because any traffic turning will have to cross the bike lane and may not see you.
  8. Consider traffic patterns when monitoring the road. For example, during rush hour, there will not only be more traffic on the roads, there will also be a higher rate of people entering and exiting driveways and parking lots, so you have to be extra cautious on both sides.

Relationships with drivers

  1. More communication is usually better. Don’t hesitate to communicate.
  2. Make noise as needed for safety reasons. Yell something at drivers to help them notice you, shout at pedestrians to watch out, whatever makes things safer. It’s better to be a little bit rude than for someone to get hurt.
  3. It’s usually better to be extra nice to people (like let them go first, let them pass you, generally try to help them) than otherwise, and it probably makes you a little safer.
  4. Signal your left or right turns with your hands. It’s safer for you if other people understand your trajectory.
  5. Drivers may try to pass you in dangerous ways. You can try to help avert catastrophes. For instance, if a car is trying to pass you from behind, and you’re ahead of them on a curve, it’s smart to signal the car with hand signals whether it’s safe to proceed. (I have seen some near misses because drivers moved into the oncoming traffic lane to pass me, but someone was coming.)
  6. Think about what messages you are sending to other vehicles because of how you ride. Sometimes I deliberately wobble just a little bit around the road, to make approaching vehicles think I might be a little bit incompetent and they should give me a little more space. Some drivers seem to pass a little closer if you are going in an even, straight line.

Failures of communication

  1. Don’t assume that drivers follow the rules about how to take turns at stop signs. A lot of people will just go once they have a brief stop, even if it isn’t supposed to be their turn.
  2. Any driver who is looking at their phone is an existential risk to your life and should be monitored with extreme caution. Such drivers probably don’t see you, their performance is impaired, and you probably can’t communicate with them at all.
  3. I am scared of self-driving cars, as a cyclist, because I don’t know how to communicate with them, or if it is even possible to communicate with them.

Parked cars

  1. Never ride close to parked cars, because their doors can open in front of you at any time, potentially causing a horrible crash.
  2. If in spite of the previous rule, you do have to ride close to parked cars, try to watch them to see if anyone is inside them. You can sometimes spot people’s heads through the rear windshields or windows, giving some clues about whether cars are occupied.
  3. If you do have to ride close to parked cars, it is also wise to slow down.

Road shapes

  1. Always leave space between yourself and the very edges of the road. You can crash if you rub up against a curb. You can also crash by slipping off the side of a roadway that is built up above the surroundings (this is more common in rural environments with thick layers of asphalt).
  2. Always cross railroad tracks at a right angle to the rails. If you approach at an oblique (near-parallel) angle, your wheel can get trapped in the groove between the rail and the roadway, causing an instant crash. (Ask me how I know.)
  3. Always be very cautious about anything in the road whose surface is nearly parallel to your direction of travel, because bike wheels are not able to safely negotiate such surfaces. For example, if there is a groove in the road that is nearly parallel to the way you are going, avoid it; your wheels can slip into it and tip you over. Cross grooved or lipped shapes at perpendicular angles if at all possible.

Relationships with pedestrians

  1. Always defer to pedestrians, but especially if they are kids, parents with strollers, or otherwise more vulnerable people.
  2. Anyone running or jogging is a special danger to bikes, because they tend to run out into the road without looking, and they move fast compared to other pedestrians.
  3. If small kids say hi to you, always say hi back to them. (This one isn’t about safety, just about humanity.)
  4. In general, bike riding can be a nice way to have some tiny, fleeting encounters with strangers, even if it’s just a smile or two in passing.

Miscellaneous risks

  1. Beware darkness. It’s easier to spot vehicles in the dark (because of their headlights), but it makes it hard to see the surface of the road in detail.
  2. Beware slippery conditions. Slippery road surfaces are probably the second most important risk factor, especially if you ride a road bike with skinny tires, since traction from the bike wheels is greatly reduced when it is raining. So, increase caution and reduce speed whenever the roads are wet or snowy. Increase caution even more when it’s cold if there is any ice on the road.
  3. Don’t carry anything in your hands while you bike. This can make it harder to handle the bike in complex moments, leading to crashes.

Gear

  1. Always wear a bike helmet (even though they are kind of annoying). My cousin died because he didn’t wear a bike helmet and someone opened their car door in his path.
  2. Get a really bright headlight. I once asked some Chicago bicycle cops what brand they used (it was ludicrously bright) and then I bought that. (For the record, it was Magic Shine).
  3. Always have a back light. Probably have it flash for extra visibility.
  4. It is strongly encouraged to have a bell, horn, or other audible signal.
  5. For extra visibility, decorate your helmet, backpack, etc, with extra reflectors, shiny patches or extra lights.
  6. If possible, wear bright or even fluorescent/high viz clothes. (I don’t always do this, but it is definitely a safety factor.)
  7. Consider environmental issues, especially on longer rides - like bring enough (or any) water if it is warm, consider sunscreen and UV protection on exposed skin, always have gloves in cool temps to keep your hands warm enough, all this. Being comfortable can become a safety factor, because discomfort can make you more agitated or inattentive.

Accidents

  1. Don’t expect that anyone will necessarily help you if you crash. People have this horrible tendency to just keep going and not… do anything to help.
  2. Maybe carry some really basic first aid stuff with you, like some bandaids in case you have minor scrapes that need covering
  3. Don’t be afraid to ask for help if you need it, especially in emergencies. One time I crashed my bike because of a sudden dip in a road at night, and I ended up staggering to the first house nearby with a light on the porch. They ended up driving me home with my bike. People can be really kind.
  4. However, sometimes people are awful and will turn you away even if you’re hurt and ask them for help. I don’t even know what to say about those people, just know that unfortunately they are out there.

Meta

  1. Commit to reducing overall risks over time, by learning better safety rules and writing mental lists like this one.
  2. Accept that biking is dangerous, no matter how you do it, but it’s worth it anyway.

Caveats:

Posted under: debugging incidents biking