Originally Posted by Eatadonut
If a car is in the right lane, how could you tell if it was going towards the exit ramp? I don't start drifting from my lane when I'm driving, so with the exception of my turn signal you'd have no indication. The only way to avoid this accident would be to assume that the cars behind you were going to turn, stop, and wait for it to be completely clear, something you don't need a mirror for.
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My commute takes me across a high speed exit as well as a high speed entrance. I consider mirrors critical -- especially for these crossings -- and won't ride without them.
Even cars that do not signal give numerous indications that they are turning. Their rate of speed frequently decreases somewhat and changes in lane position are common but not guaranteed. These changes are subtle and you're only likely to notice them with mirrors. Aside from that, you need to time your crossings to coincide with holes in the traffic. If you can't find one, you need to stop.
High speed ramps are very dangerous, and when I cross them, I spend more time looking behind than ahead. When approaching exit ramps, I typically move as far left as I can and try to "crowd" the cars. This has 2 effects. First, it makes me more visible. Secondly, it tends to cause all traffic to drift left -- this makes the traffic pattern look a little funny to people far back who can't see you yet, so hopefully it alerts them that something is different. If your mirrors show that someone isn't drifting left, you should be on full alert.
Just before I actually cross an exit ramp, I normally cut in as far as practical. This buys just a little more space so that if I miscalculate and a car does come down where I don't expect, I have enough room to take evasive maneuvers.
For my high speed on ramp, my lane positioning is opposite, but the idea is the same -- watch the cars like crazy, crowd them to improve visibility and alter the traffic flow, and cut across fast.