US and the roundabout

[booshank]

One roundabout GSJ (over US1) near Boston is large (>100m) like UK, but single lane everywhere (a major waste of space). Another near Boston (over I95) is very large (150m x 300m), 2-lane, UK-shape, but devoid of markings. Several others are semi-OK, but with strange (not necessarily bad) markings.

A lot of the very large roundabout-type junctions in New England - Massachusetts especially - are not part of the "modern roundabout" rollout in the US but come from the 1960s fad for "rotaries", which had no priority rules and were treated as fast-moving circular roadways with traffic merging as though on a freeway. Most are now converted to roundabout-type priority rules but their very large size and smooth geometry works against them.

I'm guessing Sunrise Circle in Cape Town, South Africa dates to the same sort of era (mid 20th Century) as those New England rotaries. Newer ones in SA tend to be a lot smaller. I also noticed a fair few small roundabouts in Alberta, Canada, but again none of the big, multi-lane, signalised etc things you see here.

[Chris5156]

One roundabout GSJ (over US1) near Boston is large (>100m) like UK, but single lane everywhere (a major waste of space). Another near Boston (over I95) is very large (150m x 300m), 2-lane, UK-shape, but devoid of markings. Several others are semi-OK, but with strange (not necessarily bad) markings.

A lot of the very large roundabout-type junctions in New England - Massachusetts especially - are not part of the "modern roundabout" rollout in the US but come from the 1960s fad for "rotaries", which had no priority rules and were treated as fast-moving circular roadways with traffic merging as though on a freeway. Most are now converted to roundabout-type priority rules but their very large size and smooth geometry works against them.

I'm guessing Sunrise Circle in Cape Town, South Africa dates to the same sort of era (mid 20th Century) as those New England rotaries. Newer ones in SA tend to be a lot smaller. I also noticed a fair few small roundabouts in Alberta, Canada, but again none of the big, multi-lane, signalised etc things you see here.

That’s still a roundabout, just a very big one. The geometry of the entry and exit points gives it away: it has entering traffic approaching head-on and then curving as it hits the circulatory carriageway, which is done to slow traffic on the approach and make it clear you need to give way to traffic moving around the circle. On a rotary approaching traffic smoothly merges in at high speed and the approaching road has turns as wide, if not wider, than the circulatory.