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What would you say with a constant flow of cars on the slip road? Of course I don't always move to lane 2, only when I would have to slow too much. Would you really expect me to slow 15 mph in the short time you have from seeing traffic on slip to them joining. Doesn't matter how good your observation (like most I'm keenly looking out for cars joining) often you cannot see the cars coming down the slip until they are almost joining.
Ok, play it your way and say I stay in lane 1 at a constant 70 to be whiter than white. I cannot do anything to help *all* cars merge, only time it for the one or two closest to me. The others will have to go in front or behind. Some will slip in close behind and some will cut in front. That cannot be good.
I really do not agree with your "slow considerably" comment. When? While coming under bridge just in case there are cars about to join (daft), or at the point you see the cars joining - not much time on most slips from seeing them to them joining. I wouldn't like to slow that quickly on a motorway. Of course there are many different types of slip road and some give ages of warning of joing traffic, but many do not.
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