[SoYank]

Originally Posted by spesrf25

I was reading the Motorway Speed Limit Thread and thought of this:

I'm obviously not British, so I haven't grown up using round-a-bouts all of my life. I have been here a couple of years, and I am now used to them, and they make sense in a lot of places, but what popped up in my mind is, what in the heck is the purpose of a friggin roundabout in the middle of a high-speed, high-traffic Motorway or Carriageway???? Why not have on and off ramps? All they seem to do is clogg up traffic.

There are sliproads instead of roundabouts here that do exactly what you're talking about. They are used rather effectively, too. Two examples are the A1(M)/A14(M) at The Alconburys and the A14(M)/M11 at Cambridge. There are quite a few limited interchanges that have no roundabouts involved from one motorway to another (see M1/M18).

I can not imagine the confusion and chaos and carnage that would pile up if they had put a roundabout, magic or not, at the "mixing bowl" at I-95/I-495/I-395 south of Washington, D.C. instead of the flyovers: Springfield Interchange Map. For those not familiar with this interchange, there are three or four lanes northbound, three or four lanes southbound, and two or three segregated lanes for High Occupancy Vehicles (HOV-4) that shift direction; northbound in the morning, southbound in the evening.

Originally Posted by needforspeed

Concrete is also much cheaper in other countries (e.g USA), mainly due to supply of materials, so flyovers, ramps and other structures are also cheaper.

Originally Posted by dxb335d

And a darn sight UGLIER too.

Bear in mind, though, there are some interchanges here in the UK that look like they've been imported from the U.S. For example, from ground level, the A1(M)/M18 reminds me of the US101/I-280/I-680 interchange in San Jose, California.