Comments on: Episode 25 – Highway Interchanges and SPUIs http://www.talkingtraffic.org/2008/09/09/episode-25-highway-interchanges-and-spuis/ Traffic, Transportation, and Mobility issues for the Everyday Person Fri, 18 May 2012 17:08:06 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: Bill Ruhsam http://www.talkingtraffic.org/2008/09/09/episode-25-highway-interchanges-and-spuis/#comment-94 Bill Ruhsam Tue, 09 Sep 2008 13:17:59 +0000 http://www.talkingtraffic.org/index.php/2008/09/09/episode-25-highway-interchanges-and-spuis/#comment-94 Actually, Steve, I-85 at Clairmont is a Diamond Interchange. It doesn't even qualify as a tight diamond because the ramp intersections are too far apart. ~250 to 300 feet is usually the definition of a Tight Diamond. The U-Turn loop-arounds are just an added bonus to eliminate the u-turners from the left turn movement at the signal. If you want a local Atlanta example of a SPUI, go to SR 400 and the Lenox Road (exit 2?). This is also an excellent example of why SPUIs are more expensive than diamonds. If you look at the overhead imagery (<a href="http://maps.google.com/?ie=UTF8&ll=33.851876,-84.36948&spn=0.002606,0.005686&t=h&z=18" rel="nofollow">Google Maps</a>), you can see the many additional bridge beams needed to hold up the roadway in order to give the SPUI the lane directionality it needs to operate correctly. Remember, SPUIs have one signal. If it has two, it's a Diamond. Actually, Steve, I-85 at Clairmont is a Diamond Interchange. It doesn’t even qualify as a tight diamond because the ramp intersections are too far apart. ~250 to 300 feet is usually the definition of a Tight Diamond. The U-Turn loop-arounds are just an added bonus to eliminate the u-turners from the left turn movement at the signal.

If you want a local Atlanta example of a SPUI, go to SR 400 and the Lenox Road (exit 2?). This is also an excellent example of why SPUIs are more expensive than diamonds. If you look at the overhead imagery (Google Maps), you can see the many additional bridge beams needed to hold up the roadway in order to give the SPUI the lane directionality it needs to operate correctly.

Remember, SPUIs have one signal. If it has two, it’s a Diamond.

]]> By: Steve http://www.talkingtraffic.org/2008/09/09/episode-25-highway-interchanges-and-spuis/#comment-93 Steve Tue, 09 Sep 2008 12:24:13 +0000 http://www.talkingtraffic.org/index.php/2008/09/09/episode-25-highway-interchanges-and-spuis/#comment-93 Good article. I assume that the interchange of I-85 at Clairmont Road would be a SPUI because it has the "looparound" to go back to I-85 south and I-85 south frontage road from the I-85 north onramp/frontage road? As a "roadgeek", I just wanted to make sure. :) Thanks in advance for your answer. Good article.

I assume that the interchange of I-85 at Clairmont Road would be a SPUI because it has the “looparound” to go back to I-85 south and I-85 south frontage road from the I-85 north onramp/frontage road?

As a “roadgeek”, I just wanted to make sure. :)

Thanks in advance for your answer.

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