Author Topic: Interstate 26, Eastern Terminus  (Read 296 times)

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Offline Rothman

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Interstate 26, Eastern Terminus
« on: May 24, 2017, 10:32:02 am »
Just wondering about how I-26 EB in Charleston, SC supposedly heads down the ramp for Exit 221B for Meeting St/Visitor Center/Downtown and ends just before the end of the ramp.  Does anyone have a source for that?

Offline mapmikey

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Re: Interstate 26, Eastern Terminus
« Reply #1 on: May 24, 2017, 01:18:49 pm »
I-26 east's endpoint should not have changed due to the relocation of US 17 onto the Ravenel Bridge.

The I-26 ENDS 1 MILE sign at the ramp to Exit 219B is still in its long-time location.  The endpoint should be where the highway used to split into 4 distinct lane choices (3 of which are still there) as shown in this picture:

http://www.gribblenation.com/scroads/photos/i26-exit221a-b-curley-2.jpg

Note that US 17 South does not share pavement with I-26 - it has its own ramp all the way over to the Crosstown Expwy, so I-26 must still go to the lane choices location.

I have no reason to believe I-26 goes further down the ramp to Meeting St.  In TM the endpoint splits the difference and is IMO about 1200 ft too far unless it is an average end based on what happens WB where the ramps from both directions of US 17 met to form the freeway a little further down than the EB 26 lane choices.
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Offline froggie

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Re: Interstate 26, Eastern Terminus
« Reply #2 on: May 24, 2017, 02:39:00 pm »
If anything, the endpoint should be extended slightly.  SCDOT maps and GIS shapefiles show the terminus just east of the US 17 intersections at Coming St...basically at the same spot where the Goog shows transition from surface road to freeway.  This shows that SCDOT considers I-26 to continue along the extension towards US 17 South.

However, as Mike noted, southbound US 17 does not actually share pavement with I-26 as the two legs are curb-separated until the Coming St intersection.

Offline mapmikey

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Re: Interstate 26, Eastern Terminus
« Reply #3 on: May 24, 2017, 04:00:14 pm »
If anything, the endpoint should be extended slightly.  SCDOT maps and GIS shapefiles show the terminus just east of the US 17 intersections at Coming St...basically at the same spot where the Goog shows transition from surface road to freeway.  This shows that SCDOT considers I-26 to continue along the extension towards US 17 South.

However, as Mike noted, southbound US 17 does not actually share pavement with I-26 as the two legs are curb-separated until the Coming St intersection.

This SCDOT data would contradict two things posted in the field:

The I-26 ENDS 1 MILE sign (been there 40 years or more) is 1.5 miles from the Coming St endpoint (perhaps this is splitting hairs)

Also, you pass under an Exit 221A tab well before reaching this point implying that this extended part is just an off-ramp.  And there had never been an exit tab for the King St loop ramp that is near Coming St suggesting that I-26 was still the route at that point. 

I will try to see if I can find other resources past or present that are definitive.
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Offline rickmastfan67

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Re: Interstate 26, Eastern Terminus
« Reply #4 on: May 24, 2017, 11:22:12 pm »
But don't forget the old stub ramps are still there from the old US-17 bridge.  Those could be considered the defacto place where I-26 starts/ends, and thus the current location we have would be perfect as-is.

Offline Rothman

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Re: Interstate 26, Eastern Terminus
« Reply #5 on: May 25, 2017, 08:05:10 am »
But don't forget the old stub ramps are still there from the old US-17 bridge.  Those could be considered the defacto place where I-26 starts/ends, and thus the current location we have would be perfect as-is.

This argument is basically what caused me to be a little skeptical of what is reported in Wikipedia and as our current endpoint.  I would have thought with such a significant reconstruction that the last portion of I-26 would have been adjusted in some form.

Not sure why people are arguing with Froggie, given he's looking at the actual SCDOT data? I'd lean towards changing the endpoint to how he described it and, amazingly, how Google Maps may have actually got it right.

Offline mapmikey

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Re: Interstate 26, Eastern Terminus
« Reply #6 on: May 25, 2017, 10:00:54 am »

Not sure why people are arguing with Froggie, given he's looking at the actual SCDOT data? I'd lean towards changing the endpoint to how he described it and, amazingly, how Google Maps may have actually got it right.

I'm not arguing with Froggie...I'm arguing with SCDOT - either their data is wrong or their field signage is.

Looking at more stuff, Official Maps up through 2013 do not show it extended around to Coming St (instead shows the connections around to/from Coming St as ramps).  2015 and 2016 Official maps do show it.  The latest Charleston Metro SCDOT map implies it is extended and the latest Charleston County map is inconclusive.  Just now I found the 2002 FHWA interstate table and it shows the same length (220.95) as the current table.  Coupled with no AASHTO action on I-26 this means the endpoint has never moved.  0.95 miles past the posted MM 220 does put you around the curve to Coming St.    So SCDOT in my opinion is correct on paper but is incorrect in the field.

It also means that technically if you drove I-26 east prior to the new US 17 bridge over the Cooper River and used the ramp to then-US 17 north, you did not finish the east end of I-26 and if you use the Meeting St ramp today this would also be true.  Exit signage is contrary to this and the King St ramp should be Exit 221B instead of US 17 south.

Prior to the new bridge this means there should have also been an Exit 221 on I-26 WB at the point where I-26 bent away from US 17 (where the stub ramp is still present from 17's old bridge).

This could mean the current endpoint should stay (named 221A +221) plus a new endpoint further around should be added as the endpoint and called 221B.

[modified to add the last sentence]
« Last Edit: May 25, 2017, 10:44:31 am by mapmikey »
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Offline froggie

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Re: Interstate 26, Eastern Terminus
« Reply #7 on: May 28, 2017, 08:13:27 am »
Quote
Coupled with no AASHTO action on I-26 this means the endpoint has never moved.

As I understand it, minor adjustments do not need AASHTO approval.