alt Hacker News> How do you handle an upcoming left turn (assuming right hand driving) during heavy traffic?
If I am in the middle lane (lane 2), and I realize I need to get into the leftmost lane (lane 1) to make a turn, but lane 1 is too full for me to simply move into it without affecting others, then I would have no choice but to cut someone off. I would minimize the effect in two ways: by trying to cut off whoever has left the largest gap in front of them (hunting for a gap that might not be the largest now, but will be the largest when I actually use it), and by assuming as much of the rear-end-collision risk as possible until the lane change is complete. Only once my position is optimized to begin the lane change would I signal, because signaling from a suboptimal position could scare people (or give them an opportunity to fight my ability to change lanes). If I can remain in the optimal position for a couple of blinks without any downside, I absolutely will, but in the very heavy traffic we're discussing, typically the tires hit the lane line between first and second blink -- very much not an "ask."
> Does "momentum towards closing the gap" just mean that you're keeping a higher speed than the car in front of you?
No, I was referring to the gap between the car signaling for a lane change and the car that ends up preventing the lane change, which are in two different lanes. Suppose I'm in lane 2, and a car is in lane 1 a few car-lengths ahead of me. Suppose the car in lane 1 is going slower because they just merged from a left-side entrance ramp. Due to our speed difference, after a moment they're now only 2 car-length ahead of me. Their right turn signal comes on. Now they're 1 car-length ahead of me but they haven't yet changed lanes. Now they're 0 car-lengths ahead of me (i.e., the gap is closed) and cannot change lanes. I did not "let them in" upon seeing their signal, because that would ruin my momentum.
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>If I am in the middle lane (lane 2), and I realize I need to get into the leftmost lane (lane 1) to make a turn, but lane 1 is too full for me to simply move into it without affecting others, then I would have no choice but to cut someone off.
...you could just miss your turn, instead of cutting someone off?
> Suppose the car in lane 1 is going slower because they just merged from a left-side entrance ramp.
Just to clarify, my original post was more about merging from a faster lane of travel into a slower lane, or where both lanes are traveling at about the same speed.
When merging into a faster lane I agree the slower moving car should wait for a suitable opening before signaling and merging. And there are cases where it is safer to pass a car with its blinker on than to slam on the brakes.
But also in general it's unsafe to be traveling at a large speed differential to the lane next to you. And a lot of times even though people probably could ease up a bit to make space for another car, and it would be safer to do so, they don't.