https://www.ncdot.gov/projects/liberty-road-i-40-interchange/Documents/Alternative%201%20Map%20(Diamond%20Interchange).pdf
https://www.ncdot.gov/projects/liberty-road-i-40-interchange/Documents/Alternative%202%20Map%20(Partial%20Cloverleaf%20Interchange).pdf
https://www.ncdot.gov/projects/liberty-road-i-40-interchange/Documents/Alternative%203%20Map%20(Half%20Cloverleaf%20Interchange).pdf
What interchanges are the best chosen?
Diamonds can handle high speeds going on and off, but they take up more space than the others.
Partial cloverleafs A4 or B4 are more curvy, but they don't handle high speeds.
Half cloverleads are folded diamonds, they have an advantages and disadvantages, just based on the location I guess. lol
Numbers out of a hat. Pretty sure. Studies are for amateurs.
Quote from: kphoger on March 01, 2021, 08:35:51 PM
Numbers out of a hat. Pretty sure. Studies are for amateurs.
Like why is this (https://www.google.com/maps/@35.6711845,-77.8062948,15.88z) interchange a diamond and not a folded diamond?
Cloverleafs are chosen when a more high-capacity interchange with flyovers or hybrid with flyovers and loops was initially planned, but the DOT ran dry on money (*cough* I-64/MO 364 interchange).
note that this is partially a joke
Quote from: SkyPesos on March 01, 2021, 08:41:51 PM
Cloverleafs are chosen when a more high-capacity interchange with flyovers or hybrid with flyovers and loops was initially planned, but the DOT ran dry on money (*cough* I-64/MO 364 interchange).
note that this is partially a joke
Wouldn't that mean they use braided ramps like this (https://www.google.com/maps/@35.9512618,-79.9756344,16.46z)?
They ask kernals12 for advice and then do the opposite of what he recommends.
:bigass:
I'll give a serious answer: folded diamonds are usually used when a railroad line runs immediately next to the intersecting road, since freeway ramps generally can't cross a train track at grade.
Regular diamonds are cheap and easy to build.
Quote from: US 89 on March 02, 2021, 12:12:37 AM
I'll give a serious answer: folded diamonds are usually used when a railroad line runs immediately next to the intersecting road, since freeway ramps generally can't cross a train track at grade.
That or a river/body of water
Also, folded diamonds are common on freeways for exits right near a major interchange such as this one near the I-40/I-240 interchange in east Memphis. (https://www.google.com/maps/@35.1533878,-89.8895465,1497m/data=!3m1!1e3)
Quote from: tolbs17 on March 01, 2021, 08:33:15 PM
https://www.ncdot.gov/projects/liberty-road-i-40-interchange/Documents/Alternative%201%20Map%20(Diamond%20Interchange).pdf
https://www.ncdot.gov/projects/liberty-road-i-40-interchange/Documents/Alternative%202%20Map%20(Partial%20Cloverleaf%20Interchange).pdf
https://www.ncdot.gov/projects/liberty-road-i-40-interchange/Documents/Alternative%203%20Map%20(Half%20Cloverleaf%20Interchange).pdf
What interchanges are the best chosen?
Diamonds can handle high speeds going on and off, but they take up more space than the others.
Partial cloverleafs A4 or B4 are more curvy, but they don't handle high speeds.
Half cloverleads are folded diamonds, they have an advantages and disadvantages, just based on the location I guess. lol
Why were you laughing out loud right then?
Well, there's the SPUI, which is basically a compact version of the diamond that is used on many metropolitan freeways. One advantage is that all left turns meet at the exact same spot, hence the "single-point urban interchange". But lately, the DDI (diverging diamond interchange) has become a worthy competitor as of late, with the intersecting arterial crossing over itself so that both directions are on the wrong side but the left-turn conflicts are instantly removed as a result.
I think one starts with a diamond interchange; the simplest, cheapest and most efficient way to provide access between a freeway and a surface street as their default.
Then from that basic concept, one considers all confounding factors that would make the diamond interchange sub optimal. Is the surface street parallel to railroad tracks, river or abrupt topographic change? Is there a wetland or a cemetery or a historic building nearby that the interchange should try to avoid? Is there going to be too much traffic using this interchange for the diamond to handle? Is the land expensive so one should try and minimize right-of-way? Does the surface road have other junctions nearby that would put the ramp terminals too close to the next intersection? Does the freeway have other interchanges nearby that would affect the ability of traffic to merge on and off?
Each of those confounding factors compel one to take the default diamond interchange and modify it to mitigate one or more of the confounding factors by adding loops or adding collector-distributor carriageways, or moving all the ramps to one side of the cross street, or doing something different with the ramp terminals (DDI, SPUI, roundabouts, etc.).
Eventually one arrives at a design that balances the need of the interchange to move traffic, the cost to build that interchange, and its impact on the land.
As a person who has drawn literally thousands of fictional interchanges, that is generally my process. Though not as thorough as the one the pros use, I am considering many of the same things they are. I didn't do any measuring of the wetland adjacent to my fictional interchange, but I recognize it as a wetland and if I can avoid it without adding substantial cost or complexity, I will. I don't know exactly how much things cost, but I know that some features are more expensive than other features and the more complicated something is, that generally means it's more expensive. Example: all things being equal, a loop ramp is more expensive than a straight ramp. A bridge is more expensive than a frontage road (to a certain point). A subdivision is more expensive than a farm field. That kind of thing.
Quote from: kphoger on March 02, 2021, 09:20:43 AM
Quote from: tolbs17 on March 01, 2021, 08:33:15 PM
https://www.ncdot.gov/projects/liberty-road-i-40-interchange/Documents/Alternative%201%20Map%20(Diamond%20Interchange).pdf
https://www.ncdot.gov/projects/liberty-road-i-40-interchange/Documents/Alternative%202%20Map%20(Partial%20Cloverleaf%20Interchange).pdf
https://www.ncdot.gov/projects/liberty-road-i-40-interchange/Documents/Alternative%203%20Map%20(Half%20Cloverleaf%20Interchange).pdf
What interchanges are the best chosen?
Diamonds can handle high speeds going on and off, but they take up more space than the others.
Partial cloverleafs A4 or B4 are more curvy, but they don't handle high speeds.
Half cloverleads are folded diamonds, they have an advantages and disadvantages, just based on the location I guess. lol
Why were you laughing out loud right then?
Cause I've seen regular diamond interchanges get converted into partial or folded cloverleaf/diamond interchanges.
Quote from: triplemultiplex on March 02, 2021, 01:25:46 PM
I think one starts with a diamond interchange; the simplest, cheapest and most efficient way to provide access between a freeway and a surface street as their default.
Then from that basic concept, one considers all confounding factors that would make the diamond interchange sub optimal. Is the surface street parallel to railroad tracks, river or abrupt topographic change? Is there a wetland or a cemetery or a historic building nearby that the interchange should try to avoid? Is there going to be too much traffic using this interchange for the diamond to handle? Is the land expensive so one should try and minimize right-of-way? Does the surface road have other junctions nearby that would put the ramp terminals too close to the next intersection? Does the freeway have other interchanges nearby that would affect the ability of traffic to merge on and off?
Each of those confounding factors compel one to take the default diamond interchange and modify it to mitigate one or more of the confounding factors by adding loops or adding collector-distributor carriageways, or moving all the ramps to one side of the cross street, or doing something different with the ramp terminals (DDI, SPUI, roundabouts, etc.).
Eventually one arrives at a design that balances the need of the interchange to move traffic, the cost to build that interchange, and its impact on the land.
As a person who has drawn literally thousands of fictional interchanges, that is generally my process. Though not as thorough as the one the pros use, I am considering many of the same things they are. I didn't do any measuring of the wetland adjacent to my fictional interchange, but I recognize it as a wetland and if I can avoid it without adding substantial cost or complexity, I will. I don't know exactly how much things cost, but I know that some features are more expensive than other features and the more complicated something is, that generally means it's more expensive. Example: all things being equal, a loop ramp is more expensive than a straight ramp. A bridge is more expensive than a frontage road (to a certain point). A subdivision is more expensive than a farm field. That kind of thing.
IMO, this is basically it, with the only exception being that the State (or other transportation authority) has a basic design. Most likely it is the diamond interchange, but sometimes it appears a state like NJ starts with a full cloverleaf design, and works from there.
Expected AADT of the main highway, cross street and the ramps play a big part in the design. Rural areas, where right-of-way is cheap, will have different designs than more suburban/urban areas. But, cost isn't the only concern. They're not going to (or shouldn't) skimp on cost if the ramp will be congested from day 1.
Quote from: tolbs17 on March 02, 2021, 01:38:03 PM
Cause I've seen regular diamond interchanges get converted into partial or folded cloverleaf/diamond interchanges.
1. Hmm, I guess that doesn't cause me to laugh out loud. Different strokes.
2. I hardly ever see regular diamond interchanges get converted into folded diamonds. ParClo interchanges, yes. But I think it would be strange to see one get converted into a folded diamond without some other factor like a new interchange nearby.
When California first developed freeways in the 1940s, a mixture of tight folded diamonds and simple diamond interchanges were used (Arroyo Seco Parkway/Pasadena Freeway, built originally as US 66 and now Route 110).
But there were some pre-freeway precursors with ramps already in place:
- the original MacArthur Maze, simpler than the current one but with severe merging issues
- the tight semi-directional T interchange (still existent but renovated) between US 101 and 1 in the Presidio in San Francisco
- the tight ramps on today's I-80 between Treasure Island and 5th Street, back when this was US 40/50
- the 1937-2011 Marina Boulevard/US 101 interchange in San Francisco, a simple semi-directional Y that has since been replaced with a diamond interchange
- the half-cloverleaf in SF (still in use today) between Sloat Boulevard/Route 35 and Sunset Boulevard
In the 1950s, cloverleafs were pretty much used whenever the Department of Highways wanted free-flowing interchanges, i.e. San Bernardino Freeway, Bayshore Freeway, Nimitz Freeway. This lasted into the 1970s along US 50 in the eastern parts of Sacramento County, at which point the partial cloverleaf has become the interchange of choice (usually as a cloverleaf replacement) to alleviate merge issues. Two freeway-to-freeway interchanges (I-580/I-680 and I-215/Route 60/Route 91) are vestiges of when the cloverleaf was a dominant engineering paradigm, though both have had a flyover added to try to address the design problems inherent to the basic cloverleaf layout.
The Four-Level Interchange between US 101 and what is now 110 opened in 1953 and soon became the model for modern freeway junctions (notably I-405/I-10 in the 1960s) statewide, though the most recent stack constructed is I-105/I-110. East Los Angeles Interchange on the other hand is more of an adaptive-use situation where the existing Santa Ana Freeway became a connection point for 3 other routes, rather than fitting any standardized geometry.
The US 101/I-80 junction in San Francisco is actually one of the very very few examples of a true directional T interchange in the state, possibly because of 80 and 101 originally being slated to share the Central Freeway together west to Fell Street.
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In the Philippines, due to the lack of toll-free limited access routes, trumpet junctions are common to accommodate toll booths on newer roads like the Central Luzon Link Expressway (under construction), but standard diamond and partial cloverleaf/folded diamond setups also exist, usually with toll booths on each ramp.
On the older portion of the Skyway (Buendia to Alabang), there are essentially three Y interchanges that serve a singular tollbooth (Alabang/Hillsborough, Sucat, Bicutan) similarly to a trumpet, but were specifically designed to funnel commuters to Makati in the mornings and to the south suburbs in the afternoons. (The Amorsolo flyover does this in reverse, to bring traffic into Makati's CBD from the south and outwards towards southbound traffic) NAIAX and the fully completed Buendia exit are the first two exceptions to this!
There are actually so few free-flowing interchanges so far with flyovers that one could even name an entire list of which ones in the country have them:
- Magallanes Interchange (EDSA/SLEX) in Makati
- Caloocan Interchange (Harbor Link/NLEX Connector)
- NAIAX/Skyway junction
- Tomas Claudio Interchange (Skyway/NLEX Connector), under construction
- Nagtahan Interchange (Skyway/Quirino Avenue/possibly Pasig River Expressway), under construction
- Clark North interchange off of NLEX
- Tabang Spur (former NLEX mainline)/NLEX junction
Cloverleaf junctions are so rare that each one has been named: the Balintawak Cloverleaf (which itself has a shopping mall named after it) in Quezon City between NLEX/A. Bonifacio Avenue and EDSA, and the SmartConnect Interchange in Valenzuela between NLEX and Harbor Link.
For Skyway Stage 3, almost all of the interchange choices were influenced entirely by right-of-way restrictions, notably the constrained diamond/frontage road setup at Quezon Avenue.
Ontario defaults to the Parclo A6 unless there the circumstances do not allow for the construction of a Parclo A6.
Cloverleafs, diamonds, are pretty rare here.
I mentioned this in the Chinese Highways thread, but for most freeway to surface interchanges, they default to something similar to what Texas does with a slip ramp to the frontage road and a U-turn lane at the interchange. Sometimes, there isn't a frontage road so it looks like a standard diamond. The difference is that there's a centralized signal set in the interchange instead of 2 sets, making it more like a SPUI with a ramp through movement in terms of the signaling pattern. Flyovers get added in addition to the existing diamond when traffic volumes between a certain movement justifies for them. Note that there are other variants used too, like Beijing is full of full cloverleafs from their beltways.
Quote from: SkyPesos on January 31, 2021, 05:33:05 PM
Something else I noticed with freeway interchanges in China: true diamond interchanges are rare.
On the tolled portions of the freeways, normally it's a trumpet or parclo. On the free portions in urban areas, the most common interchange looks like a diamond on a map, but functions like a SPUI with a centralized signals set. A hybrid of flyovers and loop ramps are also common for interchanges with busier arterials.
Here's an example of one of those "SPUI that looks like a diamond interchange" on Fuzhou's 2nd ring road:
- Sattelite View (https://maps.baidu.com/@13283200.671863401,2994241.3304853607,19.65z,50t/maptype%3DB_EARTH_MAP)
- Street View (note that the extended dotted lines for the lagging protected left turns may or may not be there depending on how wide the overpass is. In this case, the overpass is 4 lanes wide) (https://maps.baidu.com/@13283250.46,2994232.41,21z,87t,75.46h#panoid=09002100121906141134347147I&panotype=street&heading=260.42&pitch=-0.61&l=21&tn=B_NORMAL_MAP&sc=0&newmap=1&shareurl=1&pid=09002100121906141134347147I)