The Transportation and Mass Transit Megathread

[BnaBreaker]

1 minute ago, nashvylle said:

I don't disagree, but I was hoping for more than what was presented. 

Agreed... who couldn't write an article that essentially boiled down to arguing that the key to less traffic is... uh... less traffic.  That's the easy bit.  Haha

[nashvylle]

Music City Star goes purple 

 

[Bos2Nash]

20 hours ago, Sean blackdog said:

  Pulled from the airport thread because this is about the Donelson Pike design. Can we talk about the cluster f*** of roadway this is creating that seems very over-engineered. Can't say I'm surprised based on other interchanges around the city.

 

[PaulChinetti]

What in gods name is that thing???

[Bos2Nash]

Exactly! Your entire circle confused me with that portion being the true mind bender lol

The whole thing is a screwed up version of a diverging diamond plus a little side road that needed to tie in somewhere.

Edited May 21, 2020 by Bos2Nash

[MLBrumby]

More like a diverging banana. 

[PaulChinetti]

The theory of MOR ROADS!!!!

[BnaBreaker]

44 minutes ago, PaulChinetti said:

The theory of MOR ROADS!!!!

I guess that's one way to reduce traffic.... the goal should be one road for every car!  A chicken in every pot and a road for every car!  

[grilled_cheese]

7 hours ago, MLBrumby said:

More like a diverging banana. 

Probably designed in the early-mid-2000s so, always money in the banana stand?

[nashvylle]

15 hours ago, BnaBreaker said:

I guess that's one way to reduce traffic.... the goal should be one road for every car!  A chicken in every pot and a road for every car!  

A diet plan via buying a bigger belt. 

[donNdonelson2]

17 hours ago, Bos2Nash said:

Exactly! Your entire circle confused me with that portion being the true mind bender lol

The whole thing is a screwed up version of a diverging diamond plus a little side road that needed to tie in somewhere.

It appears to me that the “little side road” is the exit ramp from eastbound I-40 to Donelson Pike northbound.

[Bos2Nash]

13 minutes ago, donNdonelson2 said:

It appears to me that the “little side road” is the exit ramp from eastbound I-40 to Donelson Pike northbound.

I think you're right. The map below doesn't have a road there currently, so the exit just makes it all the more wonky.

[SoundScan]

So rather than simply move the Economy B Lot they're going to spend likely a quarter-billion dollars to route Donelson around it and build a massive new interchange?

[L'burgnative]

those interchanges are actually genius, it does away with all wide turns and keeps traffic flowing better.  I've used this style of interchange before and I don't think they're confusing either.  Better IMO than a round-a-bout because they're more dummy proof.

Edited May 22, 2020 by L'burgnative

[donNdonelson2]

This new interchange should provide a vast improvement to traffic flow in the area.

Edited May 22, 2020 by donNdonelson2

[PaulChinetti]

Does anyone know of anything like this in real life? @L'burgnative ?

[L'burgnative]

^Yeah they're a fairly new style interchange but there are a few around.  The only one I know of in TN is SR-66 in Sevierville into the Gatlinburg area though.  North Carolina has built a few.  I thought the Bell Rd. or Hickory Hollow exit on 24 was also going to use this style interchange as well.  Again I think they're quite genius. 

 

[Bos2Nash]

I personally like diverging diamond interchanges. They are much safer and specifically removes dangerous left turns. The way it is shown laid out on that aerial just looks confusing and dedicates a crap ton of real estate to the road.

Also the new exit ramp that continue to Donelson pike to the north could be straightened out and not create a weird merge/intersection at the diverging diamond switch.

Edited May 22, 2020 by Bos2Nash

[PaulChinetti]

Yeah based on that illustration I didn't realize that's what it was.

[Bos2Nash]

I feel like the next vision for BNA should include a MASSIVE parking structure on lots B or C and then redevelop Lot A into usable space such as hotels and such. We do not that much surface parking.

[Sean blackdog]

Today this morning from Facebook Sky5. 

[PruneTracy]

The new purple livery is a real downgrade, which is saying something.

2 hours ago, L'burgnative said:

Yeah they're a fairly new style interchange but there are a few around.  The only one I know of in TN is SR-66 in Sevierville into the Gatlinburg area though.

Alcoa Highway and Middlesettlements Road in Maryville is another extant DDI. The new Hickory Hollow Parkway interchange will be one as well as Buckner Road when it goes to construction.

TDOT tends to latch on to novel interchange treatments, so much so that you can tell when various roadways were built by the style and configuration of their interchanges. It was SPUIs in the 90s and naughty aughties, now it's DDIs.

I'm not a fan of the DDI in many of these applications as it's designed for high left-turn volumes in constrained ROW or when retrofitting an existing bridge. It's not the ideal treatment for high left-turn traffic. SR 66 needed a flyover and Buckner could easily have a loop ramp. Donelson needs a full interchange even with the airport interchange nearby. Hickory Hollow is just a wacky configuration.

[MidTenn1]

12 minutes ago, PruneTracy said:

Alcoa Highway and Middlesettlements Road in Maryville is another extant DDI. The new Hickory Hollow Parkway interchange will be one as well as Buckner Road when it goes to construction.

TDOT tends to latch on to novel interchange treatments, so much so that you can tell when various roadways were built by the style and configuration of their interchanges. It was SPUIs in the 90s and naughty aughties, now it's DDIs.

SPUI's are a good alternate to regular diamond interchanges in that they very efficiently only require 3 traffic signal phases to move all the traffic and reduces the amount of right-of-way required to build.  It has limits as to how much traffic can be moved and once built, there can be no expansion since the right-of-way is so tight to begin with.

The first DDI in Tennessee was a political choice as a certain Engineering firm in Tennessee convinced high up, non-engineering people in the Department that it was the next big  thing of the future in transportation. TDOT engineers had no input into the decision to implement it. So it was built and it really makes a nice picture on that firm's marketing brochure.

And that kiddies is how sausage gets made.

[KJHburg]

On 5/22/2020 at 1:00 PM, PaulChinetti said:

Does anyone know of anything like this in real life? @L'burgnative ?

they work really well the diverging diamond intersections and traffic moves faster.  They converted a few existing interchanges in NC to them when they widened the interstate with very few problems.  at first there was a a few heading the wrong way but honestly it is really hard to make a mistake given the barriers.  There have been no deaths or serious accidents at any of the ones in NC.  And they do move traffic faster just with some curves.

https://www.ncdot.gov/initiatives-policies/Transportation/safety-mobility/diverging-diamond-interchanges/Pages/default.aspx

[Bos2Nash]

I'm no traffic engineer, but a DDI is the closest thing to a road diet that highway interchanges could get IMO. It is designed to improve safety for all modes while still moving a high volume of traffic. The biggest drawback is probably the effect it would have on motorists who would get confused by driving on the "other side" of the road - which is something that would quickly fade.

The funky configuration of the Donelson Pike one  feels like a forced effort to utilize the DDI.