Driving during the daytime allows you to see far ahead and at a much wider angle than you can see at night. The reason why you should drive slower at night is all about vision, or rather lack thereof.
The statistics say a lot: Fifty percent of all fatalities occur after dark even though only 25 percent of all traffic moves at that time. Maybe that alone should be enough to convince the average driver to slow down at night, but perhaps a little explaining would help.
How far can I see at night?
Assuming that you have 20:20 vision and are paying attention, traveling between 55 mph and 60 mph, you will be able to come to a stop within the distance illuminated by your headlights (reflective signs shining in the distance excluded). That distance really is not very far. You are traveling about 88 feet per second.
Suppose a deer or a cow is on the roadway, and it is dark colored (and it therefore reflects much less light than lighter colored animals). What's worse, animals don't have headlights or taillights! With your low beams, you may recognize the animal at about 100-200 feet-not enough distance to brake. You just crashed into the animal or went off the road.
You always have to factor in the distance you travel during your reaction time. One to three seconds is a normal reaction time, and in that time you already traveled 88 to 250 feet. Now, the panic stop will take another three to four seconds, even though to you it will seem like an instant.
Nighttime driving safety
Don't drive faster than what your headlights can show you, a distance within which you can stop, and when road conditions worsen, slow down. Those precious seconds when you might be able to steer to safety could make all the difference.
In fog and snow, use your low beams, as the light scatter of the high beams will impair your vision and may blind oncoming traffic. If conditions don't improve, get off at the next exit and go park in a large shopping center and wait for conditions to improve.
Fog is a double-edged sword. You may not be able to see very far ahead of you, but if you slow down too much, you are likely to be mowed down by a tractor trailer speeding right along. In foggy conditions, the sooner you get off the road, the better.
During normal nighttime conditions on freeways, move with the rest of the traffic-don't speed and don't go too slowly-because traffic coming up behind you may include a driver whose vision is not 20:20.