> Cambridge also seems to have a disproportionate number of unsafe bicyclists (and pedestrians) for some reason.

There's a certain "vicious cycle" element to this. If bicycling generally appears unsafe, then mostly (over)confident, risk-tolerant people will do it. Those are the same people who are comfortable getting away with unwise things like running stoplights the wrong way at dusk on their no-brakes fixie with a single tiny red blinkie mounted high on their messenger bag. ;)

It's also tied into a common argument against biking infrastructure: "Why would we build this? There aren't any people biking now." Chicken-egg, but there are many people who won't bike if it seems unsafe. And those people have a good chance of behaving more sensibly when they are convinced to ride.