Mayor London Breed made a remarkable comment about the crash: "I'm not sure that this particular incident fits in the scope of that problem around Vision Zero but our goal is to make sure we are doing everything we can to ensure the safety of people in this city." What did she mean by that? It's hard to say but I have a guess.

Vision Zero is the idea that cities should work to reduce traffic deaths and serious injuries to zero. Obviously, an adult and a child dying and three others being injured is very severe and many street safety activists (of which I am one) reacted very negatively to Breed's apparent desire to define these deaths as outside of the goal. https://en.wikipedia.org/wiki/Vision_Zero

San Francisco committed to reach Vision Zero by 2024—this year. Here's how it's going as of last year: not well. (Source: https://sfgov.org/scorecards/transportation/traffic-fatalities)

So what did Mayor Breed mean? Some of the early reports suggest the driver may have had a medical emergency, so it's possible she meant that essentially doesn't count for the Vision Zero goal. We can't prevent medical emergencies, so putting that in the same column is unfair. Right?

If that is the Mayor's intention, I disagree with it. There are a lot of factors that seem to have played into this crash, and the medical condition of the driver before the crash is only one of them. Pointing at the medical emergency is a so-called "root cause analysis"—there is this one factor that explains the incident, and having discovered that factor, we can stop our analysis. This is not the way to reduce crashes.

What are some of the other factors (recognizing this just happened and a full analysis will take time)? The driver was driving an SUV, which is large and heavy, and car size and speed have increased in the US for years. The road is wide and fast, and allows drivers to get up to speed often. There's a mix of pedestrian, car, bus, and light rail traffic in a commercial district, creating many potential conflicts. The bus shelter apparently had no bollards (heavy poles) protecting it. And so on.

In other countries, including the Netherlands and some of the Nordic countries, a cross-disciplinary team analyzes fatal crashes and tries to recommend improvements based on their analyses. Those improvements are often applied system-wide. In the US, we usually do not do that. Instead, we use a system of "warrants" to say that *a particular intersection* must experience a high number of injuries or deaths to produce a differently-engineered street.