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Author Topic: What is a figure eight interchange?  (Read 1053 times)

Tom958

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What is a figure eight interchange?
« on: December 29, 2021, 03:58:11 PM »

I was reading this document about the development of the freeway system in Indiana and came across this on page 69 (emphasis mine):

Quote
As Interstate 465 was still the temporary terminus of Interstate 70 in February of 1972 and accident experience had been poor, the Indiana Highway Commission requested approval of the construction of a directional ramp at this interchange. An increase in travel demand in the design year had been forecast.The directional ramp was to replace the inadequate northwest loop and eliminate the serious weaving problem between the two western loops.

Here's the layout at that time. The ramp we're discussing converted the interchange into an offset cloverstack.

Quote
...At the time the interchange was originally planned, two higher-type interchanges (a full directional and a figure eight), which would not have had a weaving problem, were considered and right of way had been purchased for a full directional interchange. However, the Bureau of Public Roads found that the design year volumes did not warrant the higher cost interchanges.

According to Bing, a figure eight interchange is a dogbone roundabout interchange, and according to Google, it's a DDI. Someone here at aaroads used it for these Kentucky parkway tollbooth interchanges. Obviously, none of these is what the document I'm citing refers to.

I guess what they're referring to is any four-way system interchange with loop ramps in two opposing quadrants and direct or semidirect ramps in the other two, such as this fairly common but AFAIK unnamed layout. Or this one. Or a cloverstack. If so, I'm surprised never to have heard the term before.
« Last Edit: December 31, 2021, 05:34:35 AM by Tom958 »
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froggie

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Re: What is a figure eight interchange?
« Reply #1 on: December 31, 2021, 12:16:25 AM »

My first though was something similar to the I-91/US 5 interchange in West Springfield, MA, but that one definitely has weaving sections.
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Road Hog

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Re: What is a figure eight interchange?
« Reply #2 on: December 31, 2021, 12:36:34 AM »

I was reading this document about the development of the freeway system in Indiana and came across this on page 69 (emphasis mine):

Quote
As Interstate 465 was still the temporary terminus of Interstate 70 in February of 1972 and accident experience had been poor, the Indiana Highway Commission requested approval of the construction of a directional ramp at this interchange. An increase in travel demand in the design year had been forecast.The directional ramp was to replace the inadequate northwest loop and eliminate the serious weaving problem between the two western loops.

Here's the layout at that time. The ramp we're discussing converted the interchange into an offset cloverstack.

Quote
...At the time the interchange was originally planned, two higher-type interchanges (a full directional and a figure eight), which would not have had a weaving problem, were considered and right of way had been purchased for a full directional interchange. However, the Bureau of Public Roads found that the design year volumes did not warrant the higher cost interchanges.

According to Bing, a figure eight interchange is a dogbone roundabout interchange, and according to Google, it a DDI. Someone here at aaroads used it for these Kentucky parkway tollbooth intercanges. Obviously, none of these is what the document I'm citing refers to.

I guess what they're referring to is any four-way system interchange with loop ramps in two opposing quadrants and direct or semidirect ramps in the other two, such as this fairly common but AFAIK unnamed layout. Or this one. Or a cloverstack. If so, I'm surprised never to have heard the term before.
These are original layouts for the German Autobahnen in their original inception if I'm not mistaken, or at least what I have read in the past. Cloverleafs with two movements per loop.
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NE2

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Re: What is a figure eight interchange?
« Reply #3 on: January 02, 2022, 01:39:34 PM »

I think they're calling what was built a figure eight. Note the two loops in the southwest and northeast quadrants and the lack of weaving.
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