I always feel safest on my commute in the city between 20 and 25mph. Because the surface streets and boulevards I use have speed limits of 20-35mph, very few cars overtake me when I keep my speed up. So pretty much, if I do it right, I am riding on "empty" streets between waves of impatient motorists. Sometimes this requires running a red, other times it requires NOT GOING on a green - let the maniacs go first, then follow the last car across the light and draft him if possible or ride in the gap between the last car and the light that has now gone red again behind me.

I can't speak for European countries, or even every American city, but in mine 20+ mph is the magic number. I guess I am in a rush to survive. To some foreigner on a Dutch bike wearing wing tip shoes and a hounds-tooth sports coat I must look like I am in a hurry to get somewhere when I am actually in a hurry to get OUT OF THERE.