Similarly, the increased fatalities due to driving at night is probably primarily due to fatigue (with reduced visibility likely as the secondary cause). Notice the difference in traffic fatalities due to daylight savings time- picture study (notice the scale on the picture- it looks like it doubles and halves, but it's really just an increase or decrease of a few hundred accidents).

Indeed, all other things (including my level of tiredness) being equal, I find it easier to drive at night than during the day. (The darkness for some reason makes it easier for me to concentrate on the road and harder for me to be distracted by other stuff, it's easier for me to see distant cars (with their lights on) in the dark than in the light -- especially if the sun is shining and it has been raining -- the reflection of the sunlight on the wet road nearly blinds me.)