# US interchanges



## Ryme Intrinseca (Aug 3, 2016)

Following on from my EU interchanges thread, I've now compiled figures for the number of four-way full access freeflow interchanges in every US state. Here is a summary of results:










Some comments:

- Of 833 qualifying interchanges, 386 (46%) are _cloverleafs_. The next most common grouping is _offside_ (18%), followed by _stack_ (11%), _3 loop _ (9%) and _cloverstack_ (6%). Compared to the EU, there are far more _stacks_ but fewer _cyclic_.
- California 'wins' with 69 qualifying interchanges, followed by Texas (65), Virginia (60), Illinois (52) and New York (46). Southern California has 41, which would rank it sixth in the US were it a state.
- Florida is the third most populous state but has relatively few qualifying interchanges (23), while Alaska, Hawaii, Idaho, or Montana have none.
- In terms of state distribution of types, Texas has most _stacks _(38) and _offside_ (10), California has most _1 loop _(11) and _cloverstacks_ (13), North Carolina has most _3 loop_ (9), while Virginia has most _cloverleafs_ (47). Several states are tied for _cyclic_ (2 each) and _2 loop_ (3 each).

This is how I classified qualifying interchanges:

- _Stack_ includes classic four-level stacks, stackturbines, and stackmills.
- _Cyclic_ includes turbines as well as windmill/octopus-type designs.
- _1 loop_ refers to single loop designs, including those in a stack-like arrangement, those in a turbine-like arrangement, and those in a windmill-type arrangement.
- _Cloverstack_ refers to design with two loops in opposite corners, including 'cloverstack classic', 'clovercorner', partially-unrolled cloverleafs, cloverturbines, and clovermills.
- _2 loop_ refers to designs with two adjacent loops in either a stack, corner, turbine or windmill-like arrangement.
- _3 loop_ refers to triple loop designs in either a stack, corner, turbine, or windmill-type arrangement.
- _Cloverleaf_ includes modified cloverleafs as well as classic cloverleafs.
- _Other nearside_ refers to any design lacking offside entries or exits that does not fall into any of the above categories.
- _Offside_ refers to any design with one or more offside entries and/or exits, which I define broadly to include junctions where one of the mainlines merges or diverges (e.g. this). The _Offside_ category includes Offside stack, Offside 1 loop, Offside cloverstack, Offside 2 loop, Offside 3 loop, Divided (i.e., both mainlines split), Gothic (i.e. mainline(s) swap over), and Other offside.

_Qual_ refers to the total number of interchanges in the _Stack, Cyclic, 1 Loop, and Cloverstack_ groups. This is a good measure of the number of high quality interchanges, i.e. those lacking weaving areas and offside entries/exits. _Qual %_ is the state's percentage of the total number of quality interchanges. _Qualscore_ is the percentage of the state's interchanges that meet the quality criteria.

The table above sums the data for several subtypes. The second table provides the more detailed information by subtype:










I take the condition of 'freeflow' seriously, and disqualify interchanges with toll booths, pedestrian crossings, level crossings, traffic lights, at-grade long turns (i.e. left in a right hand traffic country), and four-way merges or diverges.


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## Exethalion (Dec 23, 2008)

Would this also exclude non signalized stackabouts like the one in Metairie?


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## Ryme Intrinseca (Aug 3, 2016)

Exethalion said:


> Would this also exclude non signalized stackabouts like the one in Metairie?


Yes, I exclude all interchanges that require a roundabout to complete movements under the 'no at-grade long turn' clause. Hence the UK only had 12 qualifying interchanges - it would have about four times that if you included stackabout-type designs!


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## Exethalion (Dec 23, 2008)

I understand your reasoning, but the behaviour of a vehicle making a left turn at a stackabout, and for example a cloverleaf with weaving (an interchange that really pushed Germany way up the rankings!) is quite similar. On a stackabout, the car must make one yielding merge at the entrance to the roundabout, then continues relatively free flowing, albeit at-grade, until it exits. On a cloverleaf it is free flowing around the loop, then has to yield/mere with the mainline or collector lane, and actually has to undergo weaving twice, if anything I would regard this as more disruptive than a single lane stackabout. Please correct me if I have missed something with this analysis.

Of course the UK chose to signalize many of their stackabouts, which I rightly agree rules them out completely. I asked because the example in Metairie is in the minority as far as this interchange design is concerned.


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## Ryme Intrinseca (Aug 3, 2016)

Exethalion said:


> I understand your reasoning, but the behaviour of a vehicle making a left turn at a stackabout, and for example a cloverleaf with weaving (an interchange that really pushed Germany way up the rankings!) is quite similar. On a stackabout, the car must make one yielding merge at the entrance to the roundabout, then continues relatively free flowing, albeit at-grade, until it exits. On a cloverleaf it is free flowing around the loop, then has to yield/mere with the mainline or collector lane, and actually has to undergo weaving twice, if anything I would regard this as more disruptive than a single lane stackabout. Please correct me if I have missed something with this analysis.


I agree with what you're saying, and had thought the same myself previously.

The problem is that if you're counting unsignalized stackabouts as freeflow, it seems like you should also count a simple at-grade roundabout with four arms as a four-way full access freeflow junction as well! Or if you add a 'grade separated' clause, you will still have to be including a basic two-bridge roundabout junction like this.

An alternative would be to discount any interchange with weaving spaces. But this would not only discount cloverleafs but three and two loop designs as well, like this for instance. These are the kind of major system interchanges that I was aiming to survey.

It's a tricky issue and I decided the best solution was just to say that roundabouts, as a type of at-grade junction, don't count.

But I do have a partial solution to the 'grade inflation' that countries like Germany get from all their cloverleafs. I now provide a 'quality' number, which is basically the total number of qualifying interchanges that lack weaving spaces or offside entries and exits (i.e. stacks, cyclic, 1 loop, and cloverstacks). Germany only has 13 interchanges of this sort, only one more than the UK.

It's not perfect but it's the best compromise I was able to find.


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## Ryme Intrinseca (Aug 3, 2016)

Data for the Midwest now added to OP


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## Jschmuck (May 27, 2008)

Ryme Intrinseca said:


> I agree with what you're saying, and had thought the same myself previously.
> 
> The problem is that if you're counting unsignalized stackabouts as freeflow, it seems like you should also count a simple at-grade roundabout with four arms as a four-way full access freeflow junction as well! Or if you add a 'grade separated' clause, you will still have to be including a basic two-bridge roundabout junction like this.
> 
> ...


Well I think what it can come down to is that roundabouts DO have posted yield signage for vehicles entering the roundabout(s), whereas MOST cloverleafs do not have posted yield signage.


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## Ryme Intrinseca (Aug 3, 2016)

Jschmuck said:


> Well I think what it can come down to is that roundabouts DO have posted yield signage for vehicles entering the roundabout(s), whereas MOST cloverleafs do not have posted yield signage.


A high proportion of cloverleafs in the US have a yield or stop sign on at least one ramp. 

Signage is also used differently between different countries, e.g. in many european countries roundabouts are not signed for a yield.

So I think using a sign-based criterion would have very undesirable effects.


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## Jschmuck (May 27, 2008)

Ryme Intrinseca said:


> A high proportion of cloverleafs in the US have a yield or stop sign on at least one ramp.
> 
> Signage is also used differently between different countries, e.g. in many european countries roundabouts are not signed for a yield.
> 
> So I think using a sign-based criterion would have very undesirable effects.


I should elaborate, I was probably referring to interstate to interstate cloverleafs, many of them do not have yield signs.


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## Ryme Intrinseca (Aug 3, 2016)

I've now completed the West region and added the results to the OP.

While the Northeast and Midwest were quite similar to each other in terms of distribution of interchanges types, with cloverleafs dominating (67% and 56% respectively), the West has a much more even distribution of types, with stacks (22%) edging out cloverstacks (19%) for the top spot. 

As that comparison suggests, interchanges in the West tend to be of higher standard designs, with a QUALSCORE (percentage of qualifying interchanges with no weaving or left hand entries/exits) of 58%, versus 7% for the Northeast and 13% for the Midwest.

On the other hand, the West had fewer qualifying interchanges (107) than the Northeast (135) or Midwest (238), despite having a higher population than either.


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## Innsertnamehere (Jun 8, 2010)

The west has less dense of a highway network, which means less intersecting freeways. It is generally a newer freeway network though, which means it has higher design standards (less cloverleafs).


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## Ryme Intrinseca (Aug 3, 2016)

I've now completed the final region (South), and therefore have data for the entire United States - see the OP.

I found 833 qualifying interchanges nationwide, with the cloverleaf unsurprisingly the most common interchange (386 or 46%), followed by offside (153), stack (94), 3 loop (73) and cloverstack (46). The state with most qualifying interchanges was California (69), followed by Texas (65), Virginia (60), Illinois (52) and New York (46).

The South had the highest regional share, with 42% of the total, a slight overperformance given it has 37% of the population. In terms of the balance of interchanges, it falls midway between the cloverleaf-dominated Midwest and Northeast and the cloverleaf-shy West. Texas has far more stacks than any other state (38), but this is counterbalanced by states like Virginia, which has the highest number of cloverleafs (47).


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## Ryme Intrinseca (Aug 3, 2016)

I've rearranged the data in the OP so it's presented for the whole US rather than by region, which is hopefully an improvement.


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## Ryme Intrinseca (Aug 3, 2016)

For California and Texas I gathered regional data as follows:










Central California corresponds to the ten counties between Stanislaus and Tulare. 

I defined East Texas and South Texas broadly, so they include Houston and San Antonio respectively, and West Texas as everything west of a line running roughly from Abilene to Del Rio.


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## Ryme Intrinseca (Aug 3, 2016)

I've now completed the survey for neighboring Canada. Here's the summary of results:










And details by subtype:










A few comments:

- Quebec comes out on top with 21 qualifying interchanges, followed by Alberta, with Ontario only in third place. This is partly explained by Ontario's preference for non-freeflow six ramp interchanges rather than full cloverleafs.
- Prince Edward Island and, surprisingly given its population, British Columbia lack any qualifying interchanges, underscoring the latter's relatively underdeveloped highway network.
- Cloverleafs accounted for half of the qualifying interchanges, with the next most common types being offside (18%) and cloverstack (10%).
- Canada's total of 60 is the same as Virginia (which ranks third in the US), and slightly behind Italy (which ranks third in Europe).


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## Kanadzie (Jan 3, 2014)

Ryme Intrinseca said:


> I've now completed the survey for neighboring Canada. Here's the summary of results:
> 
> 
> 
> ...


Ontario is really odd about cloverleafs. They built a large number in 1950's and then systematically dismantled them. Many had tight ramp configurations and performed poorly but it seems there is some kind of political thing at the transport ministry at this point. Quebec built several high-standard (with collector roads and larger ramps) cloverleaf interchanges in the 1960's and 1970's that remain fine.
I think the only "true" one left today is Hwy 62 at 401 in Belleville: https://www.google.ca/maps/place/ON...e2859e58cc3b1f0!8m2!3d44.1922357!4d-77.397808
and it's planned to be reconfigured already...


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## Burloak (Dec 21, 2014)

Kanadzie said:


> Ontario is really odd about cloverleafs. They built a large number in 1950's and then systematically dismantled them. Many had tight ramp configurations and performed poorly but it seems there is some kind of political thing at the transport ministry at this point. Quebec built several high-standard (with collector roads and larger ramps) cloverleaf interchanges in the 1960's and 1970's that remain fine.
> I think the only "true" one left today is Hwy 62 at 401 in Belleville: https://www.google.ca/maps/place/ON...e2859e58cc3b1f0!8m2!3d44.1922357!4d-77.397808
> and it's planned to be reconfigured already...


There's highway 4 and 401 in St. Thomas - which I believe is also scheduled for replacement.

https://www.google.ca/maps/@42.8538568,-81.277171,1014m/data=!3m1!1e3


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