I go slower at nights. Even on well-known roads. I'm cautious about over running my lights.

I was chuckling because I won't do mountain biking. I'm too cautious and it is too scary. But people think I am SO brave, or crazy, for biking in traffic.

Speed is just never a consideration. I might try to go faster when I'm running late but even so I know that my efforts won't make any difference in how much time it takes to get somewhere. I can't sustain the kind of output that would make a significant difference (like 5 minutes). Not in town, and not for a 3 - 5 mile trip.

The short answer is, I go as fast as I'm comfortable with for the conditions. I slow down for debris, road decay, wet, dark, fatigue, and more.