Pointlessly elaborate interchanges

[kphoger]

What the Emporia (KS) interchange used to look like.

[TheStranger]

What the Emporia (KS) interchange used to look like.

Interestingly, from Google Maps, you can still see vestiges of the original configuration today:

https://maps.google.com/maps?q=emporia,+ks&hl=en&ll=38.413332,-96.232445&spn=0.012997,0.019011&sll=37.269174,-119.306607&sspn=13.502373,19.467773&t=h&hnear=Emporia,+Lyon,+Kansas&z=16

The now-removed original trumpet dates back to the 1950s construction of the Kansas Turnpike, with the cul-de-sac to US 50 being part of the old junction:
http://www.historicaerials.com/aerials.php?scale=2.02258649687544E-05&lat=38.4138687491774&lon=-96.2347961128282&year=1959

The configuration from that topographic map above was in place as late as 2006 according to Historic Aerials.

[kphoger]

Yeah, it was only a few years ago that they reconfigured it.

Also, either I misunderstand what road feature you're referring to, or you misunderstand what a cul-de-sac is.

[TheStranger]

Also, either I misunderstand what road feature you're referring to, or you misunderstand what a cul-de-sac is.

The road marked in the topographic map heading north from US 50 that has a dead-end.   I guess that's a better way of phrasing it

[kphoger]

OK, now it all makes sense to me.  Thanks!

Looks like it's now a KTA service drive.

[johndoe]

On the Emporia example...I wonder why that wasn't originally built as a diamond. Surely they wouldn't make an extra bridge just for the fun of it.

The NSA example is interesting.  On the one hand, they reduce bridge width by not allowing the direct south to south on movement (see the interchange to the north for a bigger bridge).  But they could have reduced bridge area more by tightening the radius in the median and squaring up the bridge.  Obviously the traffic going into a roundabout doesn't need to be moving fast, why keep a bigger radius?  And the left exit and entrance probably make it worse than anything else.  Assuming there was no space to the west, wonder why they didn't shift the whole SB alignment to the east and put in a tight diamond.

[Scott5114]

On the Emporia example...I wonder why that wasn't originally built as a diamond. Surely they wouldn't make an extra bridge just for the fun of it.

Probably to route all the traffic through one toll plaza.

[J N Winkler]

On the Emporia example...I wonder why that wasn't originally built as a diamond. Surely they wouldn't make an extra bridge just for the fun of it.

Probably to route all the traffic through one toll plaza.

I don't think that can have been the reason.  Under both the original and current configurations, all traffic interfaces with the Turnpike through a single toll plaza.  That is also true of the diamond configurations that have been used elsewhere on the Turnpike, notably at Cassoday and the new Lawrence interchanges.

What I think happened is that the original designers of the Turnpike attached excessive importance to free-flow movement between the Turnpike mainline and the toll plazas, and at Emporia between the toll plaza and the various US 50 links.  This is of little benefit to traffic entering or leaving the Turnpike since the toll plaza is in all cases either an obligatory stop or a transit down a K-Tag chute which is speed-limited to 20 MPH.  In the particular case of the Emporia interchange, it sterilized a lot of ground (which is now used for KTA maintenance functions) and resulted in the necessity to maintain three superfluous grade separation structures (five were demolished when the interchange was reconfigured and only two were reinstated, both in different locations).  Also, perversely, it assigned direct routings to the low-volume movements (such as Emporia city street to Turnpike in either direction) and twisty and convoluted ones to the high-volume or long-distance movements (such as Turnpike NB to free I-35 NB or US 50 EB to Turnpike).

In short, the original design fetishized free flow at the expense of land usage, simplicity in layout, and driver expectancy.  In 1956 it would have been justified partly by the expectation that the Turnpike would be made toll-free when the bonds were paid off, since this would have removed obligatory stops at the tollbooths.  Now, almost sixty years later, it has become clear that bond renewals will prolong Turnpike tolls and with them live tollbooths for the foreseeable future.  When traffic has to stop at a toll plaza anyway, it makes little sense to shave a few seconds of time by substituting trumpet ramps (which can and do cause truck rollovers) for roundabouts or stop control at the ramp terminals.

I don't particularly welcome such a development but I can easily see the Turnpike's existing trumpet interchanges being reconstructed out of existence over the next twenty or thirty years.

[LA_MetroMan]

I'll just say any freeway to freeway interchange in Los Angeles, California.

Hey, Los Angeles has great interchanges, you can fly over them at up to 60 MPH only to reach the end and do 15 MPH on the freeway.