I was involved in what was definitely not a traffic accident and it was my fault. Ok, let me try again. What I mean is that, while we were indeed far from having an accident, our actions were also not in equilibrium and that was my fault. I didn’t do anything legally wrong, I think, but the other person involved was right to be upset about my actions. In this post I will try to explain what exactly happened in game-theoretic terms.

The situation was this: I and another person were both approaching an intersection. I was on my bike, the other person in a car. I had a stop sign in front of me and she clearly had the right of way. I was fully aware of all this and I dutifully stopped on the fat white line. So, as I said, I didn’t do anything legally wrong. My opponent in this encounter, however, also stopped. And when she stopped, she stared at me accusingly, then shook her head and eventually drove on. Why did she stop and why was she mad at me? Well, because I didn’t look at her. No, she was not offended or anything like that. The problem with me not looking at her was that she didn’t know whether I had seen her. And she was worried that I will, like many bicyclists in Graz (where I live), think that I am alone on the road and ignore the traffic signs and just keep going. She didn’t want to run me over, so she stopped.

My lack of looking at her and, thereby, not openly acknowledging her presence meant that we did not have common knowledge of the fact that I did know that she was there. I knew that she was there and she, of course, knew that she was there, but she did not know that I knew that she was there. It feels good writing things like that. Anyway, the upshot was, that she, being apparently a very considerate and careful driver and being unsure of what I would do, stopped to avoid running me over. Her action was definitely caused by me not looking at her. If I had looked at her, she would not have stopped, as she would have seen that I had seen her and, thereby, most likely rightly, assumed that I will stop.

In the end, I guess one could say that we did not play the equilibrium action profile, which would have been for me to stop and for her to breeze through the intersection. My lack of looking at her made her stop when she didn’t need to. She lost valuable time because of me and I fully understand her anger.