As mentioned, you should reduce your speed when there is heavy traffic or crappy weather. For example, this is too fast:

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However, you can also be given a citation for driving too slowly. We know, we know; like you’ll ever have that problem. But it is important to keep in mind that you must always keep the flow of traffic moving, even when conditions are less than ideal. If you’re in the middle of a blizzard, but you still find yourself driving more slowly than the rest of the traffic—even the guy on the side of the road getting his hot dog cart out of the snow has passed you up—, then you should at the very least move out of the fast, or leftmost, lane.
You should also drive more slowly if you are towing something, such as a boat, a trailer, or the awning from that last building you drove through, or if you are driving a bus, large truck, or Oscar Mayer Weinermobile.

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Although you ideally do not want to hit anyone, be especially cautious when driving near a school, as there is a high likelihood children will be present. The speed limit will usually be lower in these areas, so pay attention. Be very alert at all times near schools, playgrounds, and parks, as young children are very much like dogs and will often run suddenly into the street like complete morons. Don’t judge them, however; believe it or not, there once was a time when you too would have chosen the rescue of your foam basketball over the preservation of your own life.

Things to watch for near schools include:

• Children who are walking along or across the street or are riding their bicycles, tricycles, or motorcycles. What, you’ve never seen baby bikers?
• Crossing guards. They are not children, but they help keep children safe, so please spare them.
• School buses. Watch for flashing yellow lights, which indicate that the bus is about to stop to let out some of its passengers/prisoners. If you see flashing red lights, traffic must stop in all directions to allow the children to cross safely. If you see thousands of flashing red, yellow, and blue lights, and then the vehicle rises suddenly into the air, the bus is actually a UFO. Call one of your local media outlets to report the sighting.

You must also be very careful when approaching and driving through a blind intersection. A blind intersection is an intersection where your visibility is obscured, be it by shrubbery, buildings, parked cars, monoliths, or anything else. When coming up to such an intersection, inch forward slowly until you can clearly see that it is safe to continue. Yes, you may have to drive like a grandma for a few seconds. Get over it.

If you’re driving down an alleyway, keep it under 15 mph. Maybe even slower; you don’t want to run over any of the cats. Oh, there will be cats.