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Old May 18th, 2015, 07:30 AM   #1
pwalker
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Traffic Circles in the U.S.

Boston is known for their major traffic circles, and also known for drivers unfamiliar with them getting into major hassles.

However, I moved back to the Tri-Cities, WA (Richland, Kennewick, Pasco, WA) and this is the new western capitol of traffic circles. This area has embraced them big-time, they are indeed all over the place. They work pretty well, and local users have gained an understanding of how to use them, but some of them that have double exits (like move right for a right turn, but also a right turn lane only). This does create problems, and accidents. I would hope the traffic planners can get this right at some point.
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Old May 20th, 2015, 01:03 AM   #2
sirfreelancealot
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Quote:
Originally Posted by pwalker View Post
Boston is known for their major traffic circles, and also known for drivers unfamiliar with them getting into major hassles.

However, I moved back to the Tri-Cities, WA (Richland, Kennewick, Pasco, WA) and this is the new western capitol of traffic circles. This area has embraced them big-time, they are indeed all over the place. They work pretty well, and local users have gained an understanding of how to use them, but some of them that have double exits (like move right for a right turn, but also a right turn lane only). This does create problems, and accidents. I would hope the traffic planners can get this right at some point.
Am i right in thinking that the large 'circles' or 'rotatries' around Boston were designed for traffic to merge rather that set any particular rules about priorities - i.e. give way to traffic on the roundabout as it has priority?

When I have looked at Google Satellite images of Boston Roundabouts above or beneath major expressways, they do look like typical roundabout grade separated junctions on the UK's motorway network. When I've gone onto Streetview, there is not clear indication about who gives way to who or whether it's a case of attempring to merge and hoping for the best. Hence the accidents.

This is a typical roundabout interchange on the UK's motorway network.

https://goo.gl/maps/qinBW

Built in the 70's it has a geometry that includes tangential entry angles (i.e. pull out in a straight line to meet the curve of the roundabout) which seems to reflect the design of Boston's traffic circles. Traffic entering the roundabout usually has to give way (yield as you may say) to traffic which makes this a roundabout rather than a traffic circle.

More recent roundabouts have been designed now with more awkward entry angles - the idea being to slow traffic down as it approches the roundabout. I have an issue with this because instead of being able to pull out onto the rounbabout in a straight line you have to turn to the left to correctly place yourself in the correct circulating lane before following the roundabout to the right (obviously this is opposite in the US!). The problem is that most people go straight on anyway, drift across the roundabout lanes and sideswipe vehicles that are alongside them.

https://goo.gl/maps/twDQ6

Most roundabout junctions with motorways have become signalised to manage higher traffic levels and are now called gyratorys. Years ago this one was a simple roundabout between two motorways but it has been modified several times with traffic signals, left turn filter lanes and also with two separate direct slip-roads to bypass the roundabout. It's a junction that should have free flow links rather than a poor capacity roundabout as it becomes a major bottleneck at peak times.

https://goo.gl/maps/4zvCz

Whilst the UK is literally one of the original homes to the roundabout, a lot needs to be learned about their design what is good, what is bad and the junctions that are appropriate or otherwise to use them. The latter in these examples of where not to have a roundabout - a four level stack would have been better.
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Old May 20th, 2015, 06:28 AM   #3
pwalker
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The roundabouts in Boston are one thing. The traffic circles in the western US are something else. But the theory is the same. Avoid slowdowns by letting the motor population keep moving. For the most part, they work. However, they do take some education and getting used to. Your point about Boston is correct. There are few directional signs and newcomers can get into serious trouble in these. The roundabouts, or traffic circles in the western US are clearly marked, and it is less of a danger.
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Old May 21st, 2015, 06:36 PM   #4
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They're called a "rotary" or "rotaries" in Massachusetts. One of the unique things to the state for sure.
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