There are only 1 or 2 hazards per clip and they're REALLY obvious, if the practice clips are anything to go by. If I were to click on what I considered to be hazards, I'd come up with about 10 per clip (pedestrians, intersections, parked cars, etc.), but the CD-ROM only considered one thing to be a hazard (someone crossing the street slowly, for example).
Keep in mind that a hazard is anything that would cause you to slow down, stop, or change direction. If you keep that in mind, you won't overclick.