Traffic circles are great. Their only downside is land usage. Since we are the furthest thing from a dense city I wish they were everywhere. It would definitely suck in the short term, but people would learn.
They do get brutal when they carry more than a medium traffic load though. In Lisbon they have some 6 laners with traffic lights around them to let people in to the circle because they are too busy. These suck. A normal set of lights with dual turn lanes becomes more efficient at this point I think.
I'm not sure if its common, but one thing they do there is leave your left blinker on if you are staying in the circle, right blinker means you are leaving at your next exit. These were all over the secondary highways there and work good instead of people turning left across speeding traffic. Everyone has to slow down, so its much safer.
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