PUZZLE Answer

Several got close. Those that made guesses having to do with the sun were very warm. Anonymous was very close.

As with most traffic collision hazards, the danger lies ahead. This case, however, has the CAUSE of the danger behind. In this case, traffic looking up the hill towards a cyclist flying down the hill have the sun in their eyes even more than motorists on the flat. So far, as you can see, several of you were on track.

However, there are three sets of motorists looking up the hill towards me. The first set is off to the left on side streets and they are looking either to cross my arterial or to turn left in front of me. THEY are not a big danger because if they're turning left in front of me, they'll probably turn into the left lane and I've got lots of room. I would think the guy who didn't see me was a bit careless, but nothing more.

The second set, first flagged by Anonymous, are coming UP the hill on the arterial and make a left turn in front of me. Certainly these guys, blinded by the sun, are a concern. However, they are not the biggest danger because I get some warning if THEY turn in front of me because they have to cross another lane before they can squish me. What's more, sitting in that left turn lane, I get LOTS of warning about those guys. "Eat my dust," I smugly think.

The final group of motorists, however, are the biggest danger. These are motorists to my right, on side streets, blinded by the sun, but still hoping to make a turn onto the arterial. THESE are turning towards me (if they're turning left) and I have much less time to react to one of these motorists suddenly starting forward from the stop sign than one coming up the hill making a left turn in front of me. As noted in the comments, those signs and clutter on the right make it less easy to judge the motorist intent, and these people, as also noted, have less chance of seeing me because I'm going pretty quick down the hill, out of the sun. Even if they do, they might misjudge my speed. Equally likely, the motorist pulls forward to try to see better, and THEN notices me, and THEN panics. While I'm even further to the left of the lane than usual going down this hill (to buy that extra critical millisecond just in case), sometimes this panic involves trying to jump ahead of a fast bicycle rather than just safely staying put for a moment.

The scariest motorist of all, coming from the right hand side streets are the lawn guys, with their long trailers. They're slow and would be a hard target to miss.

Situations like this are one reason to practice quick turns. After a couple of motorists actually pulling out, adrenaline bumps up a bit each time I go down this hill and I will often slow a little when I see a motorist waiting at one of the stop signs - JUST IN CASE. One day, I'd not be surprised to come across a car-on-car collision.